Indian Journal of Chemistry Vol. 40B, September 2001, pp. 763-780

Catalytic metathesis reaction in organic synthesis

Sambasivarao Kotha* & Nampally Sreenivasachary

Department of Chemistry, Indian Institute of Technology-Bombay, Mumbai, 400 076, India

Phone: +91 -22-576 7160, Fax: +91 -22-572 3480, Email: srk@chem.iitb.ac.in

Received 27 November 2000; accepted (revised) 21 May 2001

Olefin metathesis is one of the most fascinating reac­tions in the realm of catalysis. It is a remarkable catalytic reaction in which two olefins undergo bond reorganization leading to the redistribution of alky­lidene moieties (Eqn 1 ).

Chauvin et al. la postulated that olefin metathesis proceeds by a [2+2] cycloaddition between the metal alkylidene moiety and the olefinic substrate to pro­duce a metallocyclobutane intermediate and subse­quently, cycloreversion occurs to afford a new metal alkylidene and the olefinic product (Eqn 2). In this process the fundamental steps are frequently reversi­ble and the reaction is under thermodynamic control. This process does not proceed under stereocontrol, and lead to the formation of regioisomeric mixture of olefinic products.

Olefin metathesis reaction involves both the cleav­age and the formation of C-C double bonds. A variety of homogeneous and heterogeneous catalysts are known to effect the olefin metathesis reaction and has many varied chemical applications. Recently this re­action was applied to various carbocycles and hetero­cycles.

Catalyst development Recently, a large number of homogeneous and het­

erogeneous metathesis catalysts; based on early tran­sition metal complexes with limited functional group

Rl�R2 + Catalyst •

tolerance have been reported. 1 b Since the discovery of transformation of propylene to ethylene and 2-butene over heterogeneous catalyst MO(CO)6 by Banks and Bailey in 1 964 many advances have been taken place in the utilization of metal catalysts in metathesis reac­tion. Prior to the discovery of olefin metathesis, Eleutrio reported 3 the ring opening polymerization of cycloolefins over a heterogeneous catalyst consisting of MoO supported on Ah03 at 100-400 °c. Similarly, Natta et al. successfully demonstrated4 the ring open­ing polymerization of cycloolefins over several ho­mogeneous catalyst systems such as WCI6-AlEt3 and MoCI5-AlEt3. Calderon et al. reported the develop­ment of a highly efficient homogeneous catalyst sys­tem (WCI6-AlEtCh-EtOH) for the metathesis of acy­clic 0lefins.5

Heterogeneous metathesis catalysts used as con­tacts in petrochemical industry include MoOiCoOI Ah03, WOiSi021 Ah03 and Re20i Ah03. The reaction temperature necessary for the heteroge­neous catalyst is strongly dependent on the metal where the ColMo catalyst is active at temperature as low as 1 50 °C. The early examples of olefin metathe­sis catalysts, which included a tungsten chloride or oxychloride and an alkyl metal species. These cata­lysts are less reactive to olefins due to their increased stability and yields were generally found to be low. The other established catalyst is dichlorobis(2,6-

") + C Ra R4

. . . Eqn 1

� [ ;-(� R1 R2

---- . . . Eqn 2

764 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

dibromophenoxy)oxotungsten C!z(ArOhW=O with tetra alkyllead as an activator. This system shows good functional group tolerance and has been used on several occasions.6

MeRe03 is one of the most stable and storable compounds. and it has been used as a catalyst for metathesis reaction in the synthesis of various carbo­cycles and heterocycles.7 Advances in catalyst design have contributed to the increased functional group tolerance, which inturn has expanded the scope of the olefin metathesis reaction. The key to functional group tolerance in alkene metathesis is the heightened affinity of metal alkylidenes for olefins relative to Lewis basic functionality . Most of the classical cata­lysts are rather ill-defined and more or less incom­patible with polar solvents. As a consequence, the olefin metathesis was fairly unattractive for advanced organic synthesis and also for fine chemical produc­tion over a long period of time. Now the situation has been changing with the introduction of new catalysts. In this regard, a series of transition metal complexes were developed in recent years, and a few selected examples are listed in Figure 1 (1-12).

The cyclopentadienyl titanium derivative 1 (Tebbe reagent) has been used to promote the olefin metathe­sis processes.8 In stoichiometric sense, 1 can be used to promote the conversion of carbonyl derivatives to the corresponding olefins. Both the transformations (olefination and metathesis) are thought to proceed via the reactive titanocene methylidene, which is re­leased, from the Tebbe reagent on treatment with a base.

Olefin metathesis began to receive more attention since 1 993, when Basset and co-workers developed the tungsten catalyst 2.9 This stable and sterically crowded complex with dO metal center has shown to be active catalyst system in various metathesis reac­tions such as ring-closing metathesis (RCM), enyne metathesis (EM), and ring opening metathesis (ROM) etc. The application spectrum of olefin metathesis in organic synthesis has been significantly expanded mainly due to the introduction of alkylidene metal complexes 3 and 6. Several modifications have been reported based on these catalysts including enantiom­erically pure catalyst 7 10, water soluble catalyst 5 1 1 and recyclable catalysts such as 9 and 10. 12 In addi­tion, Herrmann et al. recently presented a molecularly defined suface bound carbene precursor 8. 1 3

Alkoxy imido molybdenum complex 614 is one of the most important catalyst systems developed by Schrock and co-workers. The major advantage of this

system is its high reactivity towards a broad range of substrates with many steric or electronic variations. The alkoxy in [Mo] system can readily be altered to adjust its activity. The drawback of this catalyst is its poor functional group tolerance and high sensitivity towards air, moisture, and impurities present in the solvent.

In early 1990' s Grubbs and co-workers have re­ported a well-defined ruthenium carbene catalysts 3 and 4, and the preparation of these catalysts appears to be straightforward. Moreover, they are reasonably stable for storage, and can be handled without special equipment. 1 5 The well balanced electronic and co­ordinate unsaturation of Ru (II) carbene accounts for the high performance and excellent tolerance towards an array of polar functional groups. Recently, Grubb's and co-workers have reported the catalyst 7 which is chirally modified version of molybdenum catalyst 6. 1 6 Catalyst 7 has been used for the synthesis of various optically active carbocycles and heterocycles. Among the other catalysts, recyclable catalysts 9, and 1017 and photo inducible dichloro(p-cymene )ruthenium-(Il) dimer 11 developed by FOrstner and Ackermann are noteworthy. Hermann et al. introduced imadazolidene complexes such as 12, which can serve as a basis for the development of chiral metathesis catalysts. 1 8

The importance of carbon-carbon bond construc­tions method is evident from the huge number of publications that has been appeared with in the short period of time. In this review important recent ad­vances related to RCM, EM, ROMP, CM reaction will be discussed.

Ring-closing metathesis Catalytic ring closing metathesis (RCM) reaction

has emerged as an effective strategy in organic syn­thesis and the first example was reported as early as 1 980 by Tsuji . 1 9 Among the various types of metathe­sis conversions, RCM of a , w-dienes is particularly relevant as rapidly maturating tool for the formation of structurally diverse carbo and heterocfles of almost of any ring size. RCM inevitably cuts the molecule into two, the forward reaction is entropically driven. The equilibrium is constantly shifted towards the cy­loalkenes due to the release of highly volatile ethyl­ene. Therefore, one can promote the cyclization reac­tion by simply choosing elevated reaction temperature and/or by bubbling an inert gas through the reaction mixture. During the metathesis reaction metalcarbene complexes such as [M]=CH2 are proposed to be the catalytically active species and the reactions are

KOTHA et al. : CAT AL YTIC METATHESIS REACTION IN ORGANIC SYNTHESIS 765

PCy3 CIo... I

···Ru�. ,CI

�"/i� CI"""-- I -�Ph

PCy3 3

PCy3 C/o... I CI

;r� PCy3 Ph 4

2 OEt2

� NCMe ' ,,'\ I G:''::��u-NCMe

NCMe

8

F\ . iPr-yN-iPr CI ••.. I

' ·."Ru= ... CI ....... I ' Ph

iPr-tf'" N- 'Pr \d

1 1 12

Figure I-Various catalysts for metathesis reaction

thought to proceed according to the mechanism out­lined in Figure 2.

To date, olefin metathesis has primarily emerged as a powerful strategy and has been employed in the preparation of a wide variety of complex molecules with multiple functionalities. Due to space limitations we would like to discuss some selected examples re­lated to the synthesis of carbocycles, heterocylces, and natural products_ Our discussion here mostly fo­cused on metathesis step.

Medium ring formation by ReM There are large number of examples available for

the synthesis of varied ring sizes with less substituted olefins via RCM reaction as a key step. Studies on RCM of dicnes containing various gem-disubstituted

olefins to y ield tri and tetrasubstituted cyclic olefins are limited in number (Scheme 1).20 Cyclization of mono and gem-disubstituted dienes deliver trisubsti­tuted cyclic olefins in excellent yield with both Schrock' s catalyst and Grubb's catalyst. However, eight membered cyclic olefins are not formed with either catalyst mainly because of dimer formation was found to be predominant even under high dilution conditions (Scheme 1).2 13 However, recently few ex­amples containing eight-membered rings are re­perted.2 Ib

The scope and limitation of RCM reaction have been examined with respect to substrates containing second-row heteroatoms, including sul�hide (or disulphide) containing dienes (Scheme 11)_2

766 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

� )1<E [Ru) E = C02Et -;:? n m '-'::::

�

m E m, n =0, 1 , 2

� )1<E [Ru) E = C02Et -;:? n m '-'::::

� m ,n =0 , 1 , 2 m E

Scheme I

� [Ml=CHR� X

� � V

x = S, 99% X = S-S 77% X =O 99% X =NH 82 %

n = 1 , 2 Scheme II

1 atm H2 ..

Pd/C

C

>1�o

� 13 (-) frontalin

Scheme III

... o

Figure. 2--The mechanism of cyclization of olefin metathesis

Grubbs and co-workers have reported the total synthesis of (-) frontalin 13 via ReM reaction as a key step. In this regard, enantiopure frontalin con­taining 6,8-dioxabicyclo[3.2. 1 ] octane skeleton has been prepared in four steps from 2-methyl-4-pentene-1 ,2-diol and the key transformation using ReM as a key step is shown in Scheme 111.23

The total synthesis of (+ )-laurencin was achieved in 1 8 steps, in which the synthesis of intermediate was accomplished by ReM reaction as key step (Scheme IV)?4

Kotha reported the utility of ReM for the synthesis of cyclic a-amino acids (AAAs). The a,OJ diene was prepared in three steps from ethyl isocyanoacetate to give diene 14. The diene 14 containing AAA moiety undergoes ReM reaction in presence of Grubbs catalyst to produce cyclic AAA derivative 15 (Scheme V)?5

This methodology has also been extended by Kotha et al for post-translational peptide modification via ReM reaction as a key step (Scheme VI).26

Recently, Kotha and co-workers have developed spiro-annulation methodology via ReM reaction as a key step. The required diallylated precursors have been prepared by palladium catalyzed allylation and then subjected to ReM reaction to generate various spiro-cyclic compounds (Scheme VII).27

Hoye and co-workers have reported cyclic si­laketals with ring sizes from 7- 1 1 members via ReM reaction as a key step. Here sili tether is useful to control E/Z selectivity in the metathesis products (Scheme VIII).28

KOTHA et ai.: CAT AL YTIC METATHESIS REACTION IN ORGANIC SYNTHESIS 767

Scheme IV

NC (i-iii) < •

C02Et

O<NHAC

I C02Et 1 5

Reagents : (i) allyl bromide, K2C03, PTC (ii) HCI, EtOH (iii) AC20, CH2CI2 (iv) Grubbs catalyst

Scheme V

RCM reaction appeared to be a powerful strategy for the preparation of branched cyclitols of aminocyclitols (pseudosugars). In this regard, sugar derived l ,7-dienes are used as building blocks for the synthesis of highly functionalized cyclohexane precursors of branched cyclitols and aminocylitols (Scheme IX).29

Barrett and co-workers have prepared both mono and bicyclic 13-lactums via RCM reaction using [Mo] and [Ru] catalysts (Scheme X).30

Ghosh and co-workers recently, applied the RCM for the synthesis of a series of glucose derivatives to produce cyclopentene, hexenes, heptenes, and octenes derivatives (Scheme XI).3 1

The possiblity of forming two rings, in single reactions offers great scope for rapid synthesis of complex cyclic molecules. Although many reports by RCM reports on double ring-closing metathesis reactIons are still rare.32 Recently, Clark and Hameline reported efficiently the sythesis of trans­fused polyoxacyclic frameworks by two directional RCM reaction as a key step. (Scheme XII).33

Recently Gurjar and co-workers have reported the synthesis of cyclopentenones and bicyclic ethers derivatives via RCM as a key step (Scheme XIII).35

Vanker and co-workers reported the synthesis of pipecoline derivatives by RCM reaction as a key step (Scheme XIV).35

Metathesis reaction in supercritical CO2 Although numerous advantages are associated with

the use of supercritical carbon dioxide (scC02) as ecologically benign and user-friendly reaction me-

�NHBOC [Ru] O<NHBOC �co NH Leu:::-:'e I CO NH Leu'Ala OMe

Scheme VI

o �O ¢a0

----l .. � n ( � � n ( I Q Pd[PPh3]4 _ [Ru] n �OAc

o 0 n = 1 . 2 0

Scheme VII

Scheme VIII

dium, synthetic application to metal-catalyzed proc­esses are still rare. The efficiency and application pro­file of RCM in scC02 is noteworthy. RCM reaction in scC02 can also be carried out with substrates con­taining free amines, which are incompatible with the catalysts in solutions and the amines become reversi­bly protected in situ as the corresponding carbamic acids, which do not inhibit the active species. FOrstner repoted various ring systems by RCM under scC02 medium. The most impotant example is shown in Scheme XV. 36

768 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

?H

[Ru] ... I

HO" "p:

-:0/' .. ·· ···

Scheme IX

H�� hJX n )-N, � [Mo] )-N, /; o � 0

Scheme X

x = o, NTs, S. n = 1. 2

06� 0 •. 0Me [Ru] 0 - •• '

- I .OH Ph" " ·"O , .

. ... � Rill �

n =0, 1 . 2

Scheme XI

ReM -

Scheme XII

Scheme XIII

�� Q R �B�. RCM I( • _ R = CH:i. Ph ,..-N, �Br N [Ru] � Ph Y I ......-...... R

......-...... R Ph Ph

Scheme XIV

�O�_ScC_02-"�O o� • NH � /"'00... /'-.... /f"""-..... [Ru), [Mo) �

� ......, � I NH C:tt7 C:tt7

Scheme XV

Macrocyclization by ReM FUrstner and co-workers reported that ruthenium

carbene complex 3 can catalyze a highly efficient macrocyclization reactions of 1 , w-diene by RCM. In this regard, they also delineated guidelines contrary to previous assumptions that ring size formed and the conformational predisposition of the substrates for ring closure turned out to be of minor importance. Compound 16, readily prepared from commercially available l O-undecenoyl chloride and hex-5-en- l -01 provided 1 6-membered lactone ring in good yield (Scheme XVI).37 However, the unfunctionalized di­enes of similar length gave oligomers and no required RCM products were observed.

The concept of template directed RCM demonstrates the potential for the synthesis of various supramolecular host-guest assemblies in which either the host or the guest serves as a template for its corresponding acyclic functionalized diene Eartner (Scheme XVII). In this regard, Grubbs3 a and others38b have synthesized crowns and benzocrown derivatives by RCM reaction as a key step using ruthenium catalyst 3. The role of LiCI04 (or template) is to impose conformational constrains in the linear dienes to facilitate the RCM reaction instead of acyclic diene metathesis polymerization reaction.

Lambert and co-workers reported the synthesis of 1 8 membered macrocyclic inclusion complexes by RCM reaction as a key step (Scheme XVIII).39 Addi­tionally, they also have shown a complete geometrical control over the double bond geometry in this process.

Catanenes are interlocked molecular rings and have been synthesized by the combination of three­dimentional template effects and RCM reaction. The compound obtained by complexation of 2 equivalents

KOTHA et aI. : CATALYTIC METATHESIS REACTION IN ORGANIC SYNTHESIS 769

of the bidentate diene 17 with copper complex, which is cleanly cyclized to form the 32-membered catenate 18 by ReM in a remarkably high yield (Scheme XIX}40a Some of the earliest examples of macrocycles have been reviewed recently.4ob

RCM on a solid support Performing organic transformations on a solid

support has wittnessed an increasing popularity during the past few years.41a Olefin metathesis has also shown to be comaptible with solid support bound substrates. There are two potential strategies for ReM reaction on a solid support depending on the olefin position as depicted in Scheme XX.

The first approach (A) involves ReM of a polymer bound diene 19 resulting in the formation of cyclic product 20 which remains attached to the polymer support. In a complementary approach (B), ReM proceeds with concomitant cleavage of the substrate from the resin. Latter approach is more attractive because only compounds possesing the correct functionality will be cleaved from the solid support. Unwanted impurities will remain bound to the resin,

1 6

_[R_u1_ .....

Q«'� Compressed CO2 W

Scheme XVI

and therefore can readily be separated by filtration. Representative example of these approaches are shown in Scheme XXI.4Ib

Application of RCM in the synthesis of natural and non natural products

The relevance of ReM reaction in organic synthe­sis has been witnessed by rapidly increasing number of applications to complex target molecules including diverse natural products. Since the discovery of metal alkylidene catalysts 3 and 6 for ReM reaction, the metathesis method has been applied in a variety of natural products syntheses (Figure 3). FOrstner has applied [Ru] catalyst 3 to the asymmetric synthesis of variety of naturally occurring macrolides including exaltolide 2142 and lasiodiplodin 22.43 Epothilone A 23 synthesized both by Danishefsky44 and Nicolaou45

using ruthenium complex 3, which perhaps represents a nice illustration of ReM reaction in natural products synthesis.

FOrstner and co-workers have reported eight­membered dactylol 24 and jasmine keto lactone 2S by ReM. Another macrocyclic target molecule ap­proached using ReM is the bioactive macrolactam Sch 385 16 26 synthesized by Hoveyda group using the Schrock catalyst.46 The challenge of closing a bridging ring was also addressed by Martin and Pan­dit in the synthesis of the manzamine A core unit 27.47 Pandit has also reported a formal total synthesis of castano spermine 28 again using Ru catalyst in which the double bond was stereoselectively dihydroxylated

(�O�O�) n = 1 , 2

[Ru) 5% mol COb � 0 ,) UCIQ" CH,CI, (y�

n

Scheme XVII

Scheme XVIII

770 INDIAN ] CHEM. SEC. B. SEPTEMBER 2001

2 i [Ru]

� ii KCN

18

Scheme XIX

A � 1 9

RCM -

20

8 W� O + � Scheme XX

.0

CF�D Ph

,-O�O�N-Bn [Ru) rrNLn o �o ---. Lr0 NHBcx: NHBcx:

Scheme XXI

en route to the final product.48a Crimmins synthesized HIV reverse transcriptase inhibitor 1 592U89 29 from

I d · · 48b cyc opentene envatlve. It is clear from the above discussion, RCM

approach turned out to be very useful for the synthesis of medium-sized carbocycles and heterocycles.

Enyne metathesis Enyne metathesis is a unique and powerful strategy

and found many applications in the synthesis of inac­cessible and/or sensitive dienes. Since the discovery of enyne metathesis reaction in 1 985 by Katz many advances have been taken place in the literature.49 The main characteristic feature of this reaction is that the double bond of alkene is cleaved and each alky­lidene part is introduced onto the respective alkyne carbons forming a compound with a diene moiety. Thus, the triple bond of alkyne is converted into a single bond. This reaction occurs between alkene and alkyne, in which bond fusion and bond formation oc­curs simultaneously . This reaction is designated as a alkyledene migration reaction from the alkene part to the alkyne carbon (Figure 4).

Metal carbene complex 32 [M=CH2] will react with alkyne of enyne 30 to produce metallocyclobutene 33, a bond cleavage occurs to produce carbene complex 34 and then an intramolecular metathesis reaction with alkene occurs to provide metallacyclobutane 35 which give metathesis product 31. On the other hand, reaction proceeds via oxidative cyclization of 30 to give metallacyclopentene 36. Then reductive elimination occurs to produce cyclobutene 37 followed by bond isomerization affords compoud 31. Thus, enyne metathesis is caused by transition metal complex and the reaction can occur by various transi­tion metal catalysts and few of them are listed in Figure 5.50

Enyne metathesis reaction is of two types: (a) In­tramolecular enyne metathesis reaction and (b) Inter­molecular enyne metathesis reaction.

KOTHA et al. : CATALYTIC METATHESIS REACTION IN ORGANIC SYNTHESIS

21 Exaltolide

24 Dactylol

27 Manzamine A

RI [Ml=<

32 R:!

30

Oxidative cyclization

tv1eO

22 Lasiodiplodin

25 Jasmine Ketolactone

H�� H�

OH

28 Castanospermine

23 Epothilone A

26 Macrolactam Sch 3851 6

29 HIV reverse transcriptase inhibitor 1 592U89

Figure 3-Various natural products synthesized by ReM .

_-r--M

34 R2

Reductive elimination

Figure 4--Mechanism of eneyne metathesis reaction

77 1

772 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

Ph (CO)sW=<

OMe

Figure 5

Me (CO)sW=<

OMe ..

[FeCI4[Fe(dmf)JCI2J CH3CN, 70 0C,

E�OMe E>OJrMe

I + E I Me E Me

Scheme XXII

Intramolecular enyne metathesis Katz demonstrated that the enyne metathesis reac­

tion as a methylene migration reaction using Fischer tungsten carbene complex (Scheme XXII). The same type of reactions were subsequently reported using Fischer molybdenum and chromium carbene com­plexes and Pt, Pd, Ru based transition metal cata­lystS.5 1

Trost discovered palladium-catalyzed enyne metathesis reaction involving 1 ,6-enyne such as 38 with palladium cyclopentadiene (TePT) in presence of tri-o-tolylphosphite and dimethyl acetylenedicarboxylate leading to the formation of cycloadduct 39 and vinyl cyclopentene 40 (Scheme XXIII).52

Murai and ehatani reported the ruthenium­catalyzed skeletal reorganization of 1 ,6-enyne to viny1cy1copentene via [Rueh(eO)3h mediated isomerization reaction (Scheme XXIV).53

Enyne metathesis has also been used for the synthesis of bicyclic systems. In this regard, Grubbs543 and others54b have reported the synthesis of many cyclic and fused bicyclic [4.3.0] , [5.3.0], [4.4.0], and [5.4.0] ring systems. The reaction fails when alkyne substituent is too bulky or too electronegative groups such as TMS, BU3Sn, or a halogen (el, Br, I,). In general this reaction is a high yielding process (Scheme XXV).

Like ReM, enyne metathesis has also been used in the synthesis of various natural products as a key step. A tactical application of enyne metathesis reaction by Morl and Kinoshita involve the total synthesis of (-)­stemoamide from (-)-pyrroglutamic acid using ruthenium catalyzed enyne metathesis as a key step (Scheme XXVI).55

A novel procedure developed by Morl et aI., for synthesizing eight-membered rlng compounds using ruthenium-catalyzed enyne metathesis reaction as a key step is shown in Scheme XXVII.56

Recently, Hoye and co-workers have developed a novel method for the synthesis of (±) differolide using enyne metathesis reaction as a key step. In this regard, enyne metathesis of allylpropynoate gave 2-vinylbutenolide which readily dimarizes to (±) differolide (Scheme XXVIII).57

Barrett and co-workers have developed a useful methodology for the synthesis of bicyclic f3-lactums using enyne metathesis as a key step. In this regard, enynes with various functional groups in the tethers were subjected to metathesis reaction to give the desired bicyclic f3-lactums in good yields (Scheme XXIX).58

During the course of our investigations593 Undheim independently reported a stereoselective synthesis of cyclic l -amino- l -carboxy lic acid derivatives using

KOTHA et al. : CATALYTIC METATHESIS REACTION IN ORGANIC SYNTHESIS 773

E� :xf�PQ), E� E E 38

E

>dJcE

I + E �

E 39 40 97%

Scheme XXIII

toluene, CO, 80 oC �� 95%

Scheme XXIV

OSiEt3

/f\� �OSiEt3

� � m = I , 2

R n = I , 2 R

A = CH3, Ph, Aeaction failed when A = Bu 3Sn, TMS, Br, CI, I

Scheme XXV

o � [AU)

o -

�

Scheme XXVII

>:r-� o 0 �) Differolide

Scheme XXVIII

A

R�O [Au) ��H Steps

= \ --+ N �

-L./ 0 o (-)-Stemoamide

Scheme XXVI

ruthenium-catalyzed enyne metathesis (Scheme XXX). The starting enynes have been prepared from Schollkopf chiral auxiliary by step-wise alkylation. Subsequently, enyne metathesis using ruthenium catalyst 3 generated spiro compounds which upon hydrolysis gave dienes containing AAA moiety.59b

Kotha and co-workers have developed a new method for the synthesis of constrained AAA derivatives by a combination of enyne metathesis and Diels-Alder reaction as key steps. This methodology is conceptually new from the known methods because most of the known methods starts with preformed benzene derivatives and the present methodology involve assembling of benzene ring and thereby providing an ample opportunity to introduce the desired functionalities by choosing the appropriate dienophile (Scheme XXXI).60

As extension of the above enyne metathesis strat­egy recently Kotha and Sreenivasachary developed a novel synthesis of substituted Tic derivatives. The N­alkylated enyne building blocks were synthesized from benzophenone shicff base which upon enyne metathesis in presence of Grubb' s catalyst gave het­erocyclic inner-outer ring dienes, a useful precursors for the construction of Tic derivatives via Diels-Alder approach (Scheme XXXII).61 This methodology is conceptually new form the conventional Pictet­Spengler and Bischler-Napierlasky reaction methods because of later methods starts from the preformed benzene derivatives.

Intermolecular enyne metathesis Intermolecular enyne-metathesis is unique because

the double bond of the alkene is cleaved and each

774 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

nX� [Ru] rfQyX X = CH2, 0, NTs R-,?--� I .0 n = O, 1 , 2

o � 0 n R = H, CH3, OSiMe3 R

Scheme XXIX

=XjN-..: O�.� =X�N-..: OMe . .. 0: � �

� � . � � MeO MeO � � � MeO

'\ "- I " "

OMe iV�. N�

.............. 'CO�e R

R R reagents: i. nBuLi, THF, -78 oC, allyl bromide ii. nBuLi, propargyl bromide THF, -50 OC,

iii. benzene or toluene, 25-100 oC iv. 0.2 M aq. TFA, MeCN, RT

Scheme XXX

A � /NHAC [Au) • rr--vC02Et

�C02Et-' �NHA: " A

Scheme XXXI

�C02Et �COzEt [Ru] I - + �N...... . � N ...... Ts Ts

R

I I R

Scheme XXXII

A

�TMS I I ----.� Me�O nSu4NF, THF, MnOz, 9

Acetone 58% ex -triticene

Scheme XXXV

"11 ' I I AcO

[Ru) -

ACO� ACO�

alkylidene part is then introduced onto each alkyne carbon, respectively. When metathesis is carried out between alkene and alkyne, many olefins, dienes and polymers would be produced because intermolecular enyne metathesis includes alkene metathesis, alkyne metathesis, and enyne metathesis. Intermolecular enyne metathesis has recently been developed using ethylene gas and the alkyne (Scheme XXXIII).62

Scheme XXXIII

TMS

Scheme XXXIV

Takahashi used dibutylzirconocene as a catalyst for formal intermolecular-enyne metathesis between al­kyne and vinyl bromide (Scheme XXXIV).63

Blechert and co-workers have reported acyclic cross metathesis of olefins with alkynes to provide

R� +

KOTHA et al.: CAT AL YTIC METATHESIS REACTION IN ORGANIC SYNTHESIS

R1 = tBu, Ac R2 = Me, Et

Scheme XXXVI

OAc

+

Scheme XXXVII -4

NoOAC

E

DDQ � f¥)� NHR1

E

E =C02Me

Cli 17� Cli 17�

Cli17 + CH3 41

EtOH 9% 42 9-tricosene

Scheme XXXVIII

tBu� + �0Bn � tBu�OBn

43 44 [Mol

--+

R1 = Ph CHz-, � = Ph3, BU3 R�SnR2

Scheme XXXX

[Ru) .. R1H�R3

Scheme XXXXI

C0i'l2 R1 = Boc, Ac, Boc, Fmoc R2 = Me, Bu, H R3 = Me, Ph, Hex, Bu

�Rl [Mo) R�Rl

775

R = alkyl. CH2 TMS R1 = Ar. CN

a combination of cross-metathesis and aza Diels­Alder reaction as key steps. The reaction sequence shows atom economy and it is compatible with a variety of functionalities. This strategy has been demonstrated for a number of alkyne and alkene substrates (Scheme XXXVI).65

Scheme XXXIX

novel diene products. This methodology has been applied to the synthesis of the antifungal agent, u­triticene (Scheme XXXV).64

Blechert has also demonstated a short and efficient synthesis of highly substituted tetrahydropyridines by

Recently, Kotha and co-workers have reported the synthesis of highly functionalized phenylalanine derivatives by cross enyne-metathesis and Diels-Alder reaction as key steps (Scheme XXXVII).66

776 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

/� .... C02R [Mo]

� PhCHO, PhMe. RT

Scheme XXX XIII

(QrOH

N RCM

H 1\

�N a Mes-N N-sMe

Catalyst= CI" ,(

lyg"' " A CI/ I u=--Ph PCY3

Scheme XXXXVI

Scheme XXXXII

tJ" ""/� [Au) CID� r � n. � - - -" " "/-� � 0 � � 0 47 68%

OC - � � o--Q 48 a 92% h

n = 1 . 2, 3

Cross metathesis

Scheme XXXXIV

[Ru] or [Mo] �

Catalyst

Scheme XXXXV

There are a number of early examples of intermo­lecular metathesis between different olefins Cross Metathesis (CM) of acyclic olefins 41 and 42 pro-

vided pheromone 9-tricosene in 70% yield (Scheme XXXVIII).67

More recently, Crowe and others have shown that certain olefins undergo selective CM reaction with electronically different monosubstituted olefins in the presence of Schrock molybdenum catalyst 6 (Scheme XXXIX).68

Blechert et at. reported that CM reaction of steri­cally hindered olefins such as 39 in the presence of smaller olefins (e.g., 44) resulting in the selective CM. They also described the synthesis of functional­ized allyl stannanes employing molybdenum­catalyzed CM of terminal olefins with allyltributyl stannane and allyltriphenyl stannane respectively (Scheme XXXX).69

Gibson and co-workers reported the reaction of various protected homoallylglycine amino acid de­rivatives (e.g., 45) with aryl and alkyl substituted alkenes in presence of Ru catalyst 3 gave CM prod­ucts in good yields (Scheme XXXXI).7o

Ring opening metathesis polymerization Ring opening metathesis polymerization (ROMP)

involve for opening cyclic olefins via an in­tramolecular metathesis reaction. Historically this type of metathesis reaction has been used for produc­ing polymeric compounds. Recently, with the intro­duction of Shrock's and Grubb's catalysts, this meth-

KOTHA et al. : CAT AL YTIC MET A THESIS REACTION IN ORGANIC SYNTHESIS 777

[Ru] •

CQ?x o x = 0, NTs, CH2 50

R� [Ru]

51 •

Rif\UOR

+

�: 'T _ _ 52 53 OR

Scheme XXXXVII

odology has been applied to the synthesis of useful polymeric materials with an accelerated phase. Early examples of this reaction are relatively non-selective (Scheme XXXXII).7 1

Nomura and Schrock have shown that formation of various kinds of norbornene-based homopolymers and multiblock co-polymers such as 46 (Scheme XXXXIII).72-73

Tandem metathesis

This process involves a sequence of reactions in which a cyclic olefin undergo ROM and an in­tra/intermolecular RCM reaction. This strategy has been exemplified by Grubbs in the synthesis of a fused tricyclic ether 47. Recently, metathesis catalyst 3 has been employed for the rearrangement of styre­nyl ethers to yield isomeric heterocyclic products such as 48 (Scheme XXXXIV).74

Blechert and co-workers have reported the synthe­sis of [n.3.0] bicyclic systems involving RCM, ROM, and CM of different ring sizes and functional groups in a single domino reaction. A representative example is shown in Scheme XXXXV.75 This example clearly indicates the potential of olefin metathesis reaction in organic synthesis.

Recently, Schreiber and co-workers have synthesised complex molecule by RCM reaction as a key step (Scheme XXXXVI).76

A novel application of [Ru] catalyst 3 by Blechert and Peters is cascade of four metatheses reactions of triynes 49 to give benzene derivatives 50.77 Very re-

cently, Roy and Das reported that 2-propanyl gly­cosides such as 51 can under go a cyclotrimerization reaction in presence of catalyst 3 to give regioiso­meric glycosides 52 and 53 (Scheme XXXXVII).78

This example demonstrates the scope of acetylene cyclooligomerisation reaction in the synthesis of vari­ous annulated benzene derivatives.

Conclusions With the advent of new catalysts that can tolerate a

variety of functional groups, metathesis reaction has become an important tool in organic synthesis in re­cent times. Although there are some catalysts devel-

. h . 79 oped with regard to asymmetrIc metat eSlS , more catalysts are likely to come in near future. Advances for catalyst improvement with high turnover numbers may emerge.80 Due to space limitations it is not possi­ble to cover all these interesting aspects available in the literature.

Acknowledgement We are thankful to DST, New Delhi for the finan­

cial support. NS thank CSIR, New Delhi for the award of fellowship.

References and Notes 1 (a) Herisson J L & Chauvan Y, Makromol Chem 1 4 1 , 1970,

1 6 1 ; (b) Grubbs, R H. J Macromol Sci Chem, 1994, A3 1 , ( 1 1 ), 1 829; Schrock R R , Pure Appl Chem, 66, 1994, 1447: Ivin K J, Mol J C, Olefin Metathesis and Metathesis Polym­erization (Academic Press, New York) 1997; Calderon N, Ace Chem Res, 5, 1972, 127.

2 Banks R L & Bailey G C, lnd Engg Chem (Prod Res Dev), 3, 1964, 1 70.

3 Eleutrio H S, US Pat 3,07491 8 (1963); Ger Pat 1 ,07281 1 (1960); Chem Abstr, 1961, 55, 1 6005 h.

778 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

4 Natta G, Dall'Asta G, Mazzanti G & Motroni G, Makro­molek Chem, 69, 1963, 1 63; Natta G, Dall' Asta G & Maz­zanti G, Angew Chem Int Ed Engl, 3, 1964, 723.

5 Calderon N, Chen H Y & Scott K W, Tetrahedron Lett, 1967, 3327.

6 Nugent W A, Feldman J & Calabrese J C, J Am Chem Soc, 1 l7, 1995, 8992 and references cited therein.

7 Junga H & Blechert S, Tetrahedron Lett, 34, 1993, 373 1 ; Schneider M F, Junga H & Blechert S , Tetrahedron, 5 1 , 1995, 1 3003.

8 Stille J R. & Grubbs R H, J Am Chem Soc, 108, 1986, 855.

9 Couturier J-L, Paillet C, Leconte M, Basset J-M & Weiss K, Angew Chem Int Ed Engl, 3 1 , 1992, 628.

10 Fujimura 0 & Grubbs R H J Am Chem Soc, 1 18, 1996, 2499; Fujimura 0, de la Mata F J & Grubbs R H, Orgnometallics 15, 1996, 1 865.

I I Mohr B, Lynn D M & Grubbs R H, Orgnometallics 1 5, 1996, 4317.

12 Kingsbur J S, Harrity J P A, Bonitatebus Jr P J & Hoveyda A H, J Am Chem Soc, 1 2 1 , 1999, 791 .

13 Herrmann W A, Schattenmann W C, Nuyken 0 & Glander S C, Angew Chem Int Ed Engl, 35, 1996, 1087.

14 Schrock R R, Murdzek J S , Bazan G C, Robins J, DiMare M. & O'Regan M, J Am Chem Soc, 1 12, 1990, 3875; Fox H H, Yap K M, Robbins J, Chi S & Schrock R R, Inorg Chem, 1992, 31, 2287; Various modifications of [Mol catalyst see: Oskam J H, Fox H H, Yap K B, McCoville D H, O'Dell R, Lichtenstein B J & Schrock R R, J Organomet Chem, 459, 1993, 1 85 ; Schorock R R, Polyhedron, 14, 1995, 3 1 77; Schrock R R, Luo S, Lee J C, Zanetti N C, Davis W M & Schrock R R Macromolecules, 29, 1996, 6 1 14.

15 Nguyen S T, Johnson L K & Grubbs R H, J Am Chem Soc, 1 14, 1992, 3974; Nguyen S T, Grubbs R H & Ziller J W, J Am Chem Soc, 1 15, 1993, 9858; Schwab P, ambbs R H & Ziller J W, J Am Chem Soc, 1 1 8, 1996, 100; Wu Z, Nguyen S T, Grubbs R H & Ziller J W, J Am Chem Soc, 1 17, 1995, 5503; Schwab P, France M B, Ziller J W & Grubbs R H,

"Angew Chem Int Ed Engl, 34, 1995, 2039; Dias E L, Nguyen S T & Grubbs R H, J Am Chem Soc, 1 19, 1997, 3887; Schwab P, Grubbs R H & Ziller J W, J Chem Am Soc, 1 18, 1996, 100; Ulman M, Belderrain T R, & Grubbs R H Tetra­hedron Lett, 4 1 , 2000, 4689.

16 Fujimura 0 & Grubbs R H, J Am Chem Soc, 1 18, 1996, 2499; Fujimura 0, de la Matt F J & Grubbs R H Organomet­allics 15, 1996, 1 865.

17 FOrstner A & Ackermann L, Chem Commun, 95; 1999, FOrstner A. Angew Chem Int Ed Engl, 39, 2000, 3012.

18 Weskamp T, Schatlenmann W C, Spiegler M & Herrmann. Angew Chem Int Ed Engl, 37, 1998, 2490.

19 Tsuji J & Hashiguchi S, Tetrahedron Lett, 21, 1980, 2955.

20 Fu GC & Grubbs R H, J Am Chem Soc, 1 14, 1992, 5426; Fu G C & Grubbs R H, J Am Chem Soc, 1 15, 1993, 3800; Fuji­mura 0, Fu G C. & Grubbs R H, J Org Chem, 59, 1994,

4029; FOrstner A & Ackermann L, Chem Commun, 95; 1999, Holder S & Blechert S, Synlett 505, 1996; Grubbs R H, Miller S J & Fu G C, Acc Chem Res, 28, 1995, 446 and ref­erences cited therein.

2 1 (a) Fu G C & Grubbs R H , J Am Chem Soc, 1 15, 1992, 7324; Fu G C & Grubbs R H, J Am Chem Soc, 1 15, 1993, 3800; (b) Bourgeois D, Panerazi A, Ricard L & Prunet J, Angew Chem Int Ed Engl, 39, 2000, 726.

22 Shon Y S & Lee T R, Tetrahedron Lett, 38, 1997, 1283; Beal L M, Liu B, Chu W & Moeller K D, Tetrahedron 56, 2000, 101 1 3 .

23 Scholl M & Grubbs R H, Tetrahedron Lett, 40, 1999, 1425.

24 Crimmins M & Emmitte K A, Organic Lett, I , 1999, 2029

25 Kotha S & Sreenivasachary N, Bioorg Med Chem Lett, 8, 1998, 257

26 Kotha S, Sreenivasachary N, Mohanraja K & Durani S, Bioorg Med Chem Lett, 2001, 142.

27 Kotha S, Manivannan E, Ganesh T, Sreenivasachary N & Deb A, Synlett, 1999, 16 18.

28 Hoye T R. & Promo M A, Tetrahedron Lett, 40, 1999, 1429.

29 Sellier 0, Weghe V, deNouen D, Le Strehler C & Eustache J, Tetrahedron Lett, 40, 1999, 853; Martin R, Moyano A, Peri­cas M A & Riera A, Organic Lett, 2, 2000, 293.

30 Barrett A G M, Baugh S P D, Gibson V C, Giles M R, Mar­shall E L & Porcopiou P A, Chem Commun 1997, 155; Bar­rett A G M, Baugh S P D, Gibson V C, Giles M R, Marshall E L & Porcopiou P A, Chem Commun, 1997, 223 1 .

3 1 Holt D J , Barker W D , Jenkins P R , Davies D L, Garratt S, Fawcett J, Russel D R, Ghosh S, Angew Chem In! Ed Engl, 23, 1998, 3298; Holt D J, Barker W D, Jenkins P R, Panda J & Ghosh S, J Org Chem, 65, 2000, 482; Ghosh A K & Wang Y, Tetrahedron Lett. 4 1 , 2000, 23 19; Ghosh A K & Bilcer G, Tetrahedron Lett, 4 1 , 2000, 1003.

32 Baylon C, Heck M.-P & Mioskowski C, J Org Chem, 64, 1999, 3354; Lautens M, & Hughes G, Angew, Chem Int Ed Engl, 38, 1999, 1 29; Burke S D, Quinn K J & Chen, V J, J Org Chem, 63, 1998, 8628; Bassindale M. J, Hamley P, Leit­ner A & Harrinty J P A, Tetrahedron Lett, 40, 1999, 3247; Fu G C & Grubbs R H, J Am Chem Soc, 1 14, 1992, 7324.

33 Clark J S, & Hamelin 0, Angew Chem Int Ed Engl, 39. 2000, 372.

34 Gurjar M K, Murgaiah A M S, Cherian J & Chorghade M. S, Carbohydrate Lett, 3, 1999, 343. Gurjar M K, Ravindranath S V & Karmakar S, Chem Commun, 2001, 241 .

35 Pachamuthu K & Vanker Y D (Personal Communication).

36 FOrstner A, Koch D, Langemann K, Leitner W & Six C, Angew Chem Int Ed Engl, 36, 1997, 2466.

37 FOrstner A & Langeman K, J Org Chern, 6 1 , 1996, 3942; FOrstner A & Langeman K. J Am Chem Soc, 1 19, 1997, 9 130; FOrstner A & Langeman K, Synthesis, 79 1 , 1997, FOrstner A & Ackermann L, Chem Cornrnun, 1999, 95 ; Ka­mat V P, Hagiwara H, Katsumi T, Hoshi T, Suzuki T, &

KOTHA et al.: CATALYTIC METATHESIS REACfION IN ORGANIC SYNTHESIS 779

Ando M, Tetrahedron, 56, 2000, 4397; Hamasaki R, Funa- 1 15, 1993, 5294; Trost B M & Hashmi A S K, Angew Chern koshi S, Misaki T & Tonabe Y, Tetrahedron, 56, 2000, 7423. Int Ed Engl, 32, 1993, 1085.

38 (a) Marsella M J, Maynard H D & Grubbs R H, Angew Chern 53 Chatani N, Morimoto T, Muto T & Murai S, J Arn Chern Soc, Int Ed Engl. 36, 1997, 1 10 1 ; (b) Konig B & Hom C, Synlett 1 1 6, 1994, 6049. 1996, 1013.

54 (a) Kim S H, Bowden N & Grubbs R H, J Arn Chern Soc, 39 Ling Ng P & Lambert J N, Synlett 1999, 1749. 1 16, 1994, 1080 1 ; Kim S H, Zuercher W J, Bowden N B &

40 (a) Mohr B, Weck M, Sauvage J-P & Grubbs R H, Angew Grubbs R H, J Org Chern, 6 1 , 1996, 1073; (b) Kinoshita A &

Chern Int Ed Engl, 36, 1997, 1308; Dietrich-Buchecker C, Mori M, J Org Chern, 6 1 , 1996, 8356.

Rapenne G & Sauvage J P, Chern Cornrnun, 1997, 2053; (b) 55 Kinoshita A & Mori M, J Org Chern, 61 , 1996, 8356. FUrstner A, Topics in Catalysis, 4. 1997, 285; Schuster M & BIechert S, Angew Chern Int Ed Engl, 36, 1997, 2036. 56 Mori M, Kitamura T & Sakakibara Sato Y, Organic Lett, 2,

41 (a) Hermkens P H H, Ottenheijm H C J & Rees D, Tetrahe- 2000, 543.

dron 52, 1996, 4527; Hermkens P H H, Ottenheijm H C J & 57 Hoye T R, Donaldson S M & Vos T J, Organic Lett, 1, 1999, Rees D, Tetrahedron, 53, 1997, 5643; Fruchtel J S & Jung G, 277. Angew Chern Int Ed Engl, 35, 1996, 17; (b) Schuster M,

58 Barrett A G M, Baugh S P D, Braddock D C, Flack K, Gib-Pemerstorfer J & Blechert S, Angew Chern Int Ed Engl, 35, 1996, 1979; Peters J-U & Blechert S, Synlett 1997, 348; Van son V C & Porcopiou P A, Chern Cornrnun, 1997, 1375.

Maarseveen J H, den Hartog J A, Engelen V, Finner E, Vis- 59 (a) Kotha S, Sreenivasachary N & Brahmachary E, Tetrahe-ser G & Kresu C G, Tetrahedron Lett, 37, 1996, 8249; Pis- dron Lett, 39, 1998, 2805; (b) Hammer K & Undheim K, copio A D, Miller J F & Koch K, Tetrahedron Lett, 35, 1997, Tetrahedron, 53, 1997, 10603. 7 143; Veerman I J N, Van Maarseveen J H, Visser G M, Kruse C G, Schoemarker H E, Hiemstra H & Rutjes F P J T, 60 Kotha S, Sreenivasachary N & Brahmachary E, Eur J Org Eur J Org Chern, 1998, 2583; (c) Nicolaou K C, Winssinger Chern, 2001, 787. N, Partor J, Minkovic S, Sarabia F, He Y, Vourioumis D,

61 Kotha S, & Sreenivasachary N, Chern Cornrnun, 2000, 503; Yang Z, Li T, Giannakakou P & Hamel E, Nature, 287, 1997, 268.

Kotha S, & Sreenivasachary N, Eur J Org Chern, 2001, 0000.

42 FUrstner A & Langemann K, J Org Chern, 61, 1996, 3942. 62 Knoshita A, Sakakibar N & Mori M, J Arn Chern Soc, 1 19,

43 FUrstner A & Kindler N, Tetrahedron Lett, 37, 1996, 7005. 1997, 4561 . 44 Meng D, Su D S, Balog A, Bertinato P, Sorenson E J, Dan-

63 Takahashi T, Xi Z, Fischer R, Huo S, Xi C & Nakajima K, J ishefsky S J, Zheng Y H, Chou T C, He L & Horwitz S B, J Arn Chern Soc, 1 19, 1997, 2733.

Arn Chern Soc, 1 1 9, 1997, 4561 .

45 Nicolaou K C, He Y, Vourloumis D, Vall berg H & Yang Z, 64 Stragies R, Shuster M. & Blechert S, Angew Chern Int Ed

Angew Chern Int Ed Engl, 35, 1996, 2399. Engl, 36, 1997, 25 1 8.

46 Xu Z, Johannes C W, Salman S S & Hoveyda A H, J Arn 65 Schurer S C & Blechert S, Tetrahedron Lett, 40, 1999, 1877. Chern Soc, 1 1 8, 1996, 10926.

66 Kotha S, Halder S, Brahmachary E & Ganesh T, Synlett 47 Martin S F, Liao Y, Wong Y & Rein T, Tetrahedron Lett, 35, 2000, 853.

1994, 69 1 ; Pandit U K, Borer B C & Bieraugel H, Pure Appl 67 Rossi R, Synthesis 1 2, 1977, 8 17 ; Levisalles J, & Villemin D, Chern, 68, 1996, 659

48 (a) Overkleeft H S & Pandit U K, Tetrahedron Lett, 37, Tetrahedron, 36, 1980, 3 1 8 1 ; Crisp G T & Collis M P, Aust J Chern, 41 , 1988, 935; Quignard F, Leconte M & Basset J M,

1996, 547; (b) Crimmins M T & King B W. J Org Chern, 61 , Chern Cornrnun, 1985, 18 16; Couturier J L, Paillet C, Le-1996, 4192. r conte M, Basset J M & Weiss K, Angew Chern Int Ed EngL,

49 Katz T J & Sivavec T M, J Arn Chern Soc, 107, 1985, 737; 3 1 , 1992, 628. Sivavec T M & Katz T J, OrganornetaLLics, 8, 1989, 1620.

68 Crowe W E & Zhang Z J, J Arn Chern Soc, 1 15, 1993, 19098; 50 (a) M Mori, In Alkene Metathesis in Organic Synthesis. A Crowe W E & Goldberg D R, J Arn Chern Soc, 1 17, 1995,

Furstner Ed.; Springer, Berlin, 1998; pp 1 33-154 and refer- 5 162; Crowe W E, Goldberg D R & Zhang Z J, Tetrahedron ences cited therein; (b) Schmalz H G, Angew Chern Int Ed Lett, 37. 1996. 2 1 17. EngL, 34, 1995, 1833; Schuster M & Blechert S, Angew Chern Int Ed EngL, 36, 1997, 2036; Grubbs R H & Chang S, 69 Schuster M, Lucas N & Blechert S, Chern Cornrnun, 1997, Tetrahedron, 54, 1998, 44 13. 823.

5 1 Mori M & Watanuki S . Chern Cornrnun, 1992, 1082; Mori M 70 Gibson S E, Gibson V C & Keen S P, Chern Cornrnun, 1997, & Watanuki S, Heterocycles 35, 1993, 679; Mori M. & Wa- 1 107. tanuki S, OrganornetaLLics, 14, 1995, 5054; Katz J & Sivavec

71 Wilson S R. & Schalk D E, J Org Chern, 41 , 1976, 3928; T M, J Arn Chern Soc, 1985, 735. Rossi R, Deversi P, Lucherini A & Porri L, Tetrahedron Lett,

52 Trost B M & Tanourey G J, J Arn Chern Soc, 1 10, 1988, 1974, 879; Noels A F, Demonceau A, Carlier E, Hubert A J, 1636; Trost B M & Trost M K, J Arn Chern Soc, 1 1 3, 1991, Marquez-Silva R L & SanchezDelgado R A, J Chern Soc 1850; Trost B M, Yani M & Hoogsteen K, J Arn Chern Soc, Chern Cornrnun, 1988, 783.

780 INDIAN J CHEM, SEC. B, SEPTEMBER 2001

72 Nomura K & Schrock R R, Macromolecules, 29, 1996, 540.

73 Mortel l K H, Gingras M & Kiessleng L L, J Am Chem Soc, 1 16, 1994, 1 2053.

74 Zuercher W J, Hashimote M. & Grubbs R H, J Am Chem Soc, 1 1 8, 1996, 6634; Harrity J P A, Visser M S, Gleason J D & Hoveyda A H, J Am Chem Soc, 1 19, 1997, 1 488.

75 Stragies R & Blechert S, Synlett, 1998, 1 69.

76 Lee D, Sello J K & Schreiber S L, Org Lett, 2, 2000, 709.

77 Peters J U & B1echert S, Chem Commun, 1997, 1 983.

78 Roy R & Das K, Chem Commun, 2000, 5 19.

79 Hoveyada A H & Schrock R R, Chem Eur J, 7, 2001, 945.

80 Trnka T M & Grubbs R H, Acc Chem Res, 34, 2001, 18 .