Journal of Molecular Catalysq 39 (1987) 185 - 194 185

HYDROGENATION OF ARENES BY THE RhCls-ALIQUAT@336 CATALYST PART 3. SELECTJYE REDUCTION OF POLYCYCLIC COMPOUNDS*

IBRAHIM AMER, HAMDULLAH AMER, RACHEL ASCHER, JOCHANAN BLUM**

Department of Organic Chemistry, The Hebrew Unwerszty, Jerusalem 91904 (Israel)

YOEL SASSON

Casah Znstztute of Applred Chemzstry, The Hebrew Unwers&y, Jerusalem 91904 (Israel)

and K PETER C VOLLHARDT

Department of Chemistry, Unzverszty of Cahfornua, and the Materials and Molecular Research Dzvlslon, Lawrence Berkeley Laboratory, Berkeley, CA 94720 (US A )

(Received April 13,1986,accepted August 25,1986)

Summary

Acenaphthylene, fluorene, anthracene, phenanthrene, benz[a]an- thracene, pyrene, fluoranthene, benzo [ c] phenanthrene and some of their derivatives were shown to undergo partial hydrogenation m the presence of the RhCls-Ahquat@336 catalyst m a highly selective manner. Olefmic double bonds were found to be hydrogenated prior to aromatic moieties. In linear aromatic molecules, only the terminal rings are reduced. In phen- anthrene the C,-C,, bond and m pyrene the C4-Cs lmkage are the only ones to be affected. Benz[a] anthracene is converted exclusively into 7,8,9,- lo-tetrahydrobenz [a] anthracene. Benzo [c] phenanthrene is hydrogenated to give primarily the 5,6-dlhydro derivative. Chlorme and bromine substituents were found to undergo hydrogenolysis when attached to the reacting moi- eties, but usually remain unaffected when located on non-reacting aromatic rings

Introduction

Hydrogenation of polycychc aromatic hydrocarbons has been found to occur with certain homogeneous and heterogeneous tram&5 metal cata- lysts (see [ 2 - 111). In a few cases (e g [S] ), the processes were reported to be highly selective and consequently of particular synthetic value. We found,

*For Part 2 see [1] **Author to whom correspondence should be addressed

Q304-5102/87/$3 50 0 Elsevler Sequola/Prmted m The Netherlands

186

however, that often these reductions are of low reproduclblhty as they depend strongly on the quality of the catalysts and frequently require more severe conditions than reported m the literature.

We now wish to report that the hydrated ion pan [ (CsH,,)sNCHJ- [RhClJ, which has already proved to be an efficient lsomerlzatlon [12] and hydrogenation catalyst [ 131, promotes also regloselectlve partial hydrogena- tion of a variety of polycychc aromatic compounds under exceedingly mild conditions.

Experimental

General procedure for catalytic hydrogenation of polycychc aromatic compounds

A microhydrogenation apparatus described m our previous paper [l] was charged under nitrogen at 30 f 0.5 “C! with a mixture of 10 mg (3.79 X lo-* mmol) of RhCl,. 3H20 in 1 ml of triply distilled water, 22 mg (5.4 X lo-* mmol) of Ahquat@336, 100 ~1 (0.23 mmol) of tri-n-octylamme and 1 mmol of the freshly chromatographed substrate m 0 5 - 8.5 ml of 1,2- dlchloroethane (see Table 1). The nitrogen m the system was removed and replaced by 1 atm hydrogen. The progress of the reduction reaction was monitored both by the H, uptake and by periodic GC analysis of the reac- tion mixture. After the period given m Table 1, the hydrogenation was stopped, the organic layer separated, dried and filtered through alumina (pH = 4.5, activity I). The composition of the eluate was determined by GC-MS on a Hewlett Packard 5790 gas chromatograph equipped with a HP 5970A mass selective detector and a 25 m X 0.22 mm HP Ultra 1 cross- linked methyl silicone capillary column Quantitative separation was carried out using a preparative column packed with 15% OV-17 on Chromosorb W. The NMR spectra of the different compounds were compared with those of authentic samples New compounds obtained m this study were subJected to elemental analysis

The results obtamed with 20 polycychc aromatic substrates are sum- marized in Table 1, and selected NMR and MS data of the partially reduced products are listed m Table 2.

R 1 2R=Cl 4

3R=H

187

k

5R=H 6R=cl

R

8R=H 9R=CH,

lOR=Cl llR=Br

7

R

12R=H 13 R = CH3 14R=Cl lSR=Br 16R=OH

k

17R=CH3 18R=cl 19R=OH

21 22 23

R

24R=H 25R=Cl 26 R = Br

27 28 29

R 32 33 34R=H

35R=Cl 36

TABLE 1

Hydrogenation of various aromatlc polycychc compounds m the presence of the RhCl,* 3H+-Ahquat@336 systema

Substrate (volume of solvent, ml)

Reaction time Conversion

(h) (%) Products (yield, %)b

l(l) 4 100 3 (100) 2 (1) 72 90 3 (92), 4 [141(8) 3(l) 72 82 4 (100) 5 (1) 72 19 7 [15] (100) 6 (1) 72 37 5 (51), 7 (42) 8 (6) 30 20 12 [16] (100) 9 (1) 72’ 52 13 [17] (100)

10 (1) 24 100 14d (1oo)e 11 (2) 76 95 15 [18] (100) 20 (3) 48 72 16 [19] (89), 19 [19] (11) 21(8 5) 264 100 22f (88), 23 (12) 24 (0 5) 1449 1 27 (100) 25 (1) 75 19 24 (89), 27 (8) 26 (0 5) 36 37 24 (95), 27 (5) 28 (1) 90 84 24 (lo), 27 (24),

29 [20] (60) 30 (3) 48 95 31 [6] (100) 32 (1) 122 28 33 [6] (100) 34 (1) 168g 19 36 [21] (8431 35 (3) 144 50 34 (go), 36 (10) 37 (1) 72 54 38 [22] (62), 39 [23] (21)

40 [24] (ll), 41’ (5)

aReactlon conditions 1 mmol substrate, 3 79 X 10V2 mmol RhC13*3Hz0 m 1 ml trlply distilled water, 5 4 X lop2 mmol Ahquat@336, 0 23 mmol trl-n-octylamme m the indicated volume of 1,2-dlchloroethane, hydrogen pressure 1 atm, T = 30 f 0 5 “C bThe references given are those according to which authentic samples have been prepared CExtenslon of the reaction period to 90 h gave a 5 1 mixture of 13 17 [ 251

(contmued)

189

dM p 45 - 46 “C, elemental analysis found C, 77 28, H, 6 00, Cl, 16 46% Calculated for C1,$I&l C, 77 59, H, 6 00, Cl, 16 39% When the reaction was conducted for 48 h a 1 1 ratio of 14 18 was obtained M p of 18 62 - 64 “C, elemental analysis found C, 76 60, H, 8 02%, calculated for C#&l C,

76.36, H, 7 72% fM p 102 - 103 “C elemental analysis found C, 83 66, H, 6 75%, calculated for C&1$ C,8400,H,650% sSome catalyst deterioration was noticed durmg the process hOccaslonally traces of hexahydrofluoranthene were also formed ‘As a mixture of two Isomers

TABLE 2

200/300 MHz NMR and 70 eV EI mass spectral data for some partially hydrogenated aromatic polycychc compounds

Compound Spectral data

4 NMR (CDC~S)~ 1 345 - 2 362 (m, 6, H2, H3, H4), 2 642 - 2 922 (m, 5, Hl, H2a, H5), 6 901 (dd, 1, J6,,= 5 8 Hz, Ja,s= 2 2 Hz, H6), 7 041 (m,

2, H7, H8), MSC .m/z.(rel mtenslty) 158 (29), 157 (9), 130 (loo), 129 (42), 128 (27), 127 (9), 115 (41)

12

13

14

15

7 NMR (CDCl# 1 150 - 1 653 ( 6, Hl, H2, H3), 1 822 (m, 2, H4), m, 2 455 (m, 1, H9a), 2 577 (dd, 1, Jgem= 15 1 Hz, J9,9a = 4 8 Hz, H9), 2 853 (dd, 1, Jgem = 15 1 Hz, J9’,9a = 6 6 Hz, H9’), 3 092 (dt, 1, J4,4a = 5 8 Hz, J4a,9a = 5 9 Hz, H4a), 7 214 (m, 4, H5, H6, H7, H8)

NMR (C$,)b 1 603 (m, 4, H2, H3), 2 726 (m, 4, Hl, H4), 7 268 (dd, 2, J5,6 = J,,8 = 6 2 Hz, J5,,= J6,s = 3 2 Hz, H6, H7), 7 375 (s, 2, H9, HlO),

MSd J5,6 J,,, 192 J5,, 178 167 166 165 7 640 (dd, 2, = = 6 2 Hz, = J6 = 3 2 Hz, H5, H8), s

m/z (rel intensity) (loo), (lo), (35), (19),

(36), 155 (lo), 154 (73), 153 (42), 152 (37), 191 (12), 141 (57), 139 (ll), 127 (14), 115 (19), 89 (13)

NMR (CDC~S)~ 1 762 - 2 033 (m, 4, H2, H3), 2 590 (s, 3, (X3), 2 943 (t, 1, J1,2= 6 8 Hz, Hl), 3 013 (t, 1, J5,4 = 6 5 Hz, H4), 7 421 (m, 2, H6, H7), 7 484 (s, 1, HlO), 7 751 (d, 1, J7,8 = 7 6 Hz, HS), 8 051 (d, 1, Jsq6 = 7 8 Hz, H5),

Msd m/z 196 181 179 (14), 178 (17), 167 (rel intensity) (loo), (98),

(20), 166 (30), 165 (51), 155 (18), 153 (23), 152 (28), 151 (9), 141 (9), 128 (lo), 115 (12), 89 (12)

NMR (C6Ds)a 0 728 (m, 4, H2, H3), 1 987 (t, 2, J3,4= 6 6 Hz, H4), 2 282 (t, 2, J1,2= 7 1 Hz, Hl), 7 192 (s, 1, HlO), 7 312 (m, 2, H6, H7), 7 591 (dd, 1, J5,6= 9 4 Hz, J5,,= 1 8 Hz, H5), 8 578 (dd, 1, J6,s= 1 5 Hz, J,,* = 9 2 Hz, HS),

Msd m/z 218 216 188 182 (15), 181 (rel Intensity) (33), (loo), (19), (94), 179 (21), 178 (23), 177 (ll), 176 (ll), 175 (15), 166 (41), 165 (57), 153 (30), 152 (39), 151 (19), 150 (ll), 139 (ll), 89 (16)

NMR (C6D6jb 1 615 (m, 4, H2, H3), 2 708 (t, 2, J3,4= 7 0 Hz, H4), 2 969 (t, 2, J1.2 = 6 4 Hz, Hl), 7 300 (s, 1, HlO), 7 394 (m, 2, H6, H7), 7 607 (d, 1, J5,6 = 7 7 Hz, H5), 8 526 (d, 1, J7,8 = 8 5 Hz, H8)

(contmued)

190

TABLE 2 (contmued)

Compound Spectral data

16 NMR (CDCl# 1 749 (m, 4, H2, H3), 2 605 (m, 2, Hl or H4), 2 903 (m, 2, Hl or H4), 4 361 (s, 1, Ofi), 7 802 (dd, 2, Js,~= J~,s= 5 8 Hz, J5,,= J6,8= 3 3 Hz, H6, H7), 8 310 (dd, 2, J5,6= J,,a= 5 8 Hz, J5,,=

Js,s= 3 3 Hz, H6, H7), 8 310 (dd, 2, Js,a= J,,3 = 5 8 Hz, J5,,= J6,3= 3 3 Hz, H5, H8), 8 333 (s, 1, HlO)

17 NMR (C,Db)b 1 718 (m, 4, H2, H7), 1807 (m, 4, H3, H6), 2 057 (s, 3, (X3), 2 619 (t, 4, J1,2 = J7,3 = 6 2 Hz, Hl, HS), 2 697 (t, 4, 53.4 = J5,6 = 6 2 Hz, H4, H5), 6 648 (s, 1, HlO), MSd m/z 200 197 185 172 157 (rei mtenslty) (59), (19), (loo), (21), (20), 143 (27), 142 (16), 141 (17), 134 (21), 129 (15), 128 (20), 115

(10)

18

19

22

23

29

31

NMR (CDCl# 1 764 (m, 8, H2, H3, H6, H7), 2 698 (t, 4, J3,4= J5,6= 5 6 Hz, H4, H5), 2 730 (t, 4, J1,2 = J7,3 = 6 0 Hz, Hl, H8), 6 726 (s, 1,

HlO), MF m/z (rel Intensity) 222 (32), 220 (95), 192 (21), 186 (50), 185 (loo), 179 (13), 177 (16), 169 (9), 157 (28), 156 (12), 143 (77), 142 (29), 141 (43), 115 (38), 99 (100)

NMR (CDCIS)~ 1 803 (m, 8, H2, H3, H6, H7), 2 594 (t, 4, J3,4= J5,6 = 6 0 Hz, H4, H5), 2 695 (t, 4, J1,2= J,,3= 5 9 Hz, Hl, H8), 4 618 (s, 1, Og), 6 463 (s, 1, HlO)

NMR (CDCl# 1860 (m, 4, H2, H3), 2 944 (m, 4, Hl, H4), 7 121 (ddd, 1, J5,, = 2 6 Hz, J,,3= 10 2 Hz, J7,= = 8 8 Hz, H7), 7 290 (dd, 1, J,,3 = 10 2 Hz, Js,= = 2 5 Hz, H8), 7 453 (s, 1, H9), 7 501 (s, 1, HlO), 7 660 (dd, 1, J5,,= 2 6 Hz, J5,F = 8 6 Hz, H5), Msd m/z (rel intensity) 200 (58), 199 (17), 198 (50), 197 (39), 196 (30), 184 (IO), 183 (50), 182 (loo), 181 (20), 178 (ll), 177 (7), 176 (7), 172 (20), 171 (lo), 170 (lo), 167 (26), 166 (14), 165 (27), 159 (ll), 154 (41), 153 (19), 152 (18), 141 (29), 128 (5), 115 (5)

NMR (CDCl# 3 915 (s, 4, H9, HlO), 6 830 - 7 027 (m, 2, H5, HS), 7 158 - 7 261 (m, 5, Hl, H3, H4, H6, H7), MSd m/z (rel intensity) 198 (95), 197 (loo), 196 (60), 194 (16), 183 (16), 178 (8), 177 (12), 176 (7), 175 (5), 170 (7), 98 (7).

NMR (CD&NY 2 619 (s, 4, H9, HlO), 7 029 - 7 112 (m, 5, Hl, H5, H6, H7, H8), 7 548 (d, 1, J1,? = 6 6 Hz, H2), 7 583 (s, 1, H4),

MSC m/t (rel intensity) 216 (29), 214 (87), 213 (9), 180 (15), 179 (loo), 178 (91), 177 (20), 176 (24), 152 (12), 151 (ll), 89 (32), 88

(22), 76 (22)

NMR (C&)’ 1 797 (m, 4, HlO, H9), 2 908 (m, 2, H8), 2 979 (m, 2, Hll), 7 550 (m, 3, H2, H3, H7), 7 674 (6, 2, H5, H6), 7 822 (dd, 1, J2,4= 2 2 Hz, J3,4= 8 2 Hz, H4), 8 423 (s, 1, H12), 8 634 (dd, 1, J1,2 = 8 4 Hz, J1,3 = 1 9 Hz, Hl),

MSC m/z (rel intensity) 232 (loo), 231 (lo), 230 (lo), 229 (lo), 228 I”d”,‘;,“l; (12), 215 (ll), 204 (87), 202 (15), 191 (13), 116 (7), 114 (6),

(contmued)

191

TABLE 2 (contmued)

Compound Spectral data

33 NMR (CDC13)a 3 495 (s, 4, H4, H5), 7 596 - 7 677 (m, 4, H2, H3, H6, H7), 7 751 (s, 2, H9, HlO), 7 904 (dd, 2,J1,2 = J,,8= 7 8 Hz, J1,3= J6,8= 1 5 Hz, Hl, HS), MSd m/z (rel 204 203 202 (79), 200 101 intensity) (88), (103), (23), (40), 100 (22), 88 (10)

36

38

39

40

NMR (CDC13)a 7 044 (d, 1, J4,5 = 7 5 Hz, H4), 7 228 - 7 384 (m, 3, H5, H8, H9), 7 530 (d, 2, J5,6= Jg,lo= 7 1 Hz, H6, HlO), 7 744 (d, 1, J7,8= 6 7 Hz, H7), MSd m/z (rel intensity) 206 (47), 205 (17), 203 (13), 202 (15), 189 (8), 179 (16), 178 (loo), 176 (lo), 165 (8), 152 (8), 89 (12), 88 (16), 76 (10)

NMR (C6Ds)a 2 631 (s, 4, H5, H6), 7 148 - 7 323 (m, 6, H3, H4, H7, H8, HlO, Hll), 7 547 (dd, 1, J1,2= 7 7 Hz, J2,3= 8 3 Hz, H2), 7 703 (d, 1, Jg,l,,= 9 4 Hz, H9), 7 895 (d, 1, J1,2 = 7 7 Hz, Hl), 8 549 (d, 1, J11,12 = 8 4 Hz, H12), MSd m/z (rel mtenslty) 230 (loo), 229 (74), 228 (39), 227 (19), 226 (27), 215 (31), 202 (18), 114 (12), 113 (13), 101 (9)

NMR (C6D6)a 1 562 (m, 2, H3), 1 697 (m, 2, H2), 2 608 (s, 4, H7, H8), 2 776 (t, 2, J3,‘, = 6 5 Hz, H4), 2 954 (t, 2, J1,? = 6 1 Hz, Hl), 6 807 (AB system, 2, JAB = 7 3 Hz, H5, H6), 7 342 (m, 3, H9, HlO, Hll), 7 608

(d, 1, JII,IZ = 7 7 Hz, H12), MSd m/z (rel mtenslty) 234 (loo), 219 (lo), 215 (8), 207 (8), 206 (45), 205 (29), 204 (ll), 203 (23), 202 (25), 193 (19), 192 (18), 191 (57), 190 (20), 189 (24), 179 (14), 178 (26), 165 (9), 152 (8), 101 (8)

NMR (CSD~)~ 1 259 - 1 788 (m, 4, H6, H7), 2 112 (m, 1, H6a), 2 610 (t, 4, J5,6= J7,s= 5 8 Hz, H5, H8), 3.789 (d, JhhlZb = 5 2 Hz, H12b), 7 040 (m, 8, Hl, H2, H3, H4, H9, HlO, Hll, H12), Msd m/z (rel Intensity) 234 (74), 215 (7), 207 (15), 206 (84), 204 (7), 203 (12), 202 (14), 191 (23), 189 (lo), 179 (9), 178 (20), 165 (lo), 152 (7), 143 (69), 141 (14), 130 (42), 129 (loo), 128 (64), 117 (26), 115 (33), 105 (lo), 102 (7), 101 (ll), 91 (34), 89 (10)

4lA MSd m/z (rel intensity) 240 (8), 147 (6), 146 (8), 145 (23), 144 (21), 143 (24), 141 (7), 131 (16), 130 (52), 129 (loo), 128 (44), 127 (lo), 117 (12), 116 (9), 115 (29), 104 (6), 91 (17)

41B MSd m/z (rel intensity) 240 (73), 212 (6), 198 (18), 197 (loo), 184 (18), 183 (52), 169 (ll), 167 (9), 165 (13), 158 (9), 155 (21), 154 (lo), 153 (lo), 152 (12), 144 (12), 143 (13), 142 (14), 141 (49), 130 (7)

aRecorded on a Bruker WP 200 instrument bRecorded on a Bruker WH-300 instrument =Mass spectrum taken on a Varlan MAT 311 instrument dMass spectrum taken on a GC-MS Hewlett Packard 5790 gas chromatograph equipped with a HP 5970 A mass selective detector and a HP Ultra 1 capdlary column

192

Results and discussion

As for the RhClsAhquat@336-promoted hydrogenation of naph- thalenes [ 11, also the reduction of polycyclzc aromatlc compounds takes place m dlstmctlve steps and, threfore, 1s of considerable synthetic utlhty. Table 1 indicates that the various polycychc aromatics not only differ m their reactlvltles but also afford different types of hydroaromatlc products depending on the structural constramts of the substrates.

Olefmlc bonds present m the aromatic substrates are always the fast to be hydrogenated Thus, e g , mdene IS mltlally converted m quantitative yield mto mdane, and acenaphthylene (1) gves acenaphthene (3) prior to its conversion mto the hexahydro compound (4).

Polycycl~cs that are composed of lmearly fused aromatlc rings are hydrogenated exclusively at the termmal rings, mdlcatmg kinetic control of the course of the reactlon For example, anthracene (8) 1s transformed at first entvely to the 1,2,3,4-tetrahydro-derlvatlve (12), while further reduction gwes 1,2,3,4,5,6,7,&octahydroanthracene. In this respect, our anthracene hydrogenation differs from most other reported homogeneous processes m which 9,10-dlhydroanthracene 1s formed either as the sole or the mam product (see e g [ 51). The refractory behavior of the central ring towards Hz m the presence of the rhodmm catalyst could be demonstrated by introduction of a hydrolyzable group at the 9 posltlon While the chlorine atoms m chlorobenzene [13] and chloronaphthalene [l], as well as in 5- chloroacenaphthene (2) and 4-chlorofluorene (6)) are ehmmated mostly przor to the saturation of the aromatic rings, the halogen atoms m 9-chloro- and 9-bromo-anthracene (10, 11, respectively) are completely retamed durmg reduction to the correspondmg tetrahydro-compounds 14 and 15. Even upon prolonged treatment with hydrogen that leads to the reduction of both terminal rings, no ehmmatlon of the halogen atom takes place 9Xhloroanthracene (10) can therefore be converted mto the pure octa- hydro derivative, 18.

Chlorme and bromine on the terminal rings are, of course, hydro- genolyzed Fluorine, however, resists hydrogenation (cf the conversion of fluorobenzene mto fluorocyclohexane [13]), but its presence causes some reduction also at the meso posltlons 2Xluoroanthracene (21) yields, m addition to 22, also 2-fluoro-9,10-dlhydroanthracene (23) as a minor prod- uct.

9-Anthrone reacts as the enol tautomer to give 1,2,3,4_tetrahydro- anthracen-9-01 (16) m the first stage, and the octahydro derivative 19 upon further hydrogenation.

In contrast to anthracenes, phenanthrene derivatives are hardly affected at then terminal rings. Phenanthrene (24) itself forms no 1,2,3,4_tetrahydro compound, but is reduced extremely slowly (1% m 144 h) at the 9,10-poa- tions. We attribute this behavior to the sterlc constraints of the nearly over- lapping hydrogen atoms of the bay region (C, and C,). Halogen substltuents enhance the rate of hydrogenation of phenanthrene. However, as the reac-

193

tlon takes place at Cg and ClO, the 9-chloro- and 9-bromo-compounds (25, 26) give only the halogen-free products 24 and 27. On the other hand, the halogen m 3-chlorophenanthrene (28), which 1s attached to a nonreact- mg ring, is therefore affected only slightly durmg the hydrogenation process, and 3-chloro-9,lOdlhydrophenanthrene (29) 1s the mam reaction product.

The difference m the reactivity between the linear and angular terminal rmgs can be observed also during the reaction of benz[a]anthracene (30). This compound gves exclusively 8,9,10,11-tetrahydrobenz[a]anthracene (31) and cannot be hydrogenated further under our standard reaction con- ditions

As m phenanthrene, no reaction takes place at the 1,2 and 3 posltlons of pyrene (32) The C,-C, bond 1s the only one to be reduced.

Benzo[c]phenanthrene (37), which can be regarded formally as a combmatlon of two overlappmg phenanthrene molecules, forms, as ex- pected, 5,6-dlhydrobenzo [c] phenanthrene (38) as the chief primary prod- uct However, m this system some further hydrogenation already starts before complete consumption of the starting material to give 1,2,3,4,7,8- and czs-5,6,6a,7,8,12b-hexahydrobenzo [c] phenanthrene (39 and 40 respec- tively). Both the malor secondary product 39 and the minor one 40, still absorb hydrogen and yield two lsomerlc dodecahydrobenzo [ c] phenanthrenes (41) (separated by GC-MS).

It is notable that although 38 contams one isolated benzene ring and one naphthalene structure, the hydrogenation of this compound takes place only at one of the naphthalene rings. The mam process occurs on the ‘non- substituted’ naphthalene ring, as one could predict from the results of our previous studies [ 11.

A similar difference between the reactivity of a benzene and a naph- thalene moiety m a polycychc molecule 1s found m the hydrogenations of fluoranthene (34) and 3-chlorofluoranthene (35), which @ve the 1,2,3,10b- tetrahydro compound (36) rather than the 6b,7,8,9,10,10a-hexahydro derivative

Finally, the high stereoselectlvlty m the formation of two fused hydro- aromatic rmgs should be noted. Both m the reduction of fluorene (5) to 1,2,3,4,4a,9a-hexahydrofluorene and m the generation of 40 from 38, the czs-fused structures are the only ones formed

Acknowledgement

We are grateful to the U.S -Israel Bmatlonal Science Foundation for Financial support of this study.

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194

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