Exam III Key 2016 - Home - Chemistry · Part II. Lautens, M.; Colucci, J. T.; Hiebert, S.; Smith,...
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1 CHEMISTRY 850 Exam III December 15, 2016 KEY NAME (Print) Question Max Points Score * 1 15 __10.6 2 10 ___6.1 3 10 ___5.5 4 15 ___4.6___ 5 10 ___9.1 6 10 ___6.2___ 7 10 ___6.0___ 8 15 __11.9___ 9 10 ___5.5___ 10 15 ___8.7__ 11 10 ___5.4___ 12 10 ___7.6___ 13 10 ___6.3___ Exam Total 150 ___95.6___ * average over 11 exams
Transcript of Exam III Key 2016 - Home - Chemistry · Part II. Lautens, M.; Colucci, J. T.; Hiebert, S.; Smith,...
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CHEMISTRY 850
Exam III December 15, 2016
KEY
NAME (Print)
Question Max Points Score *
1 15 __10.6
2 10 ___6.1
3 10 ___5.5
4 15 ___4.6___
5 10 ___9.1
6 10 ___6.2___
7 10 ___6.0___
8 15 __11.9___
9 10 ___5.5___
10 15 ___8.7__
11 10 ___5.4___
12 10 ___7.6___
13 10 ___6.3___
Exam Total 150 ___95.6___
* average over 11 exams
2
1) Propose a mechanism for the following reaction (15 pts).
Part I
Cong, Z.-Q.; Wang, C.-I.; Chen, T.; Yin, B.-Z. Synth. Commun. 2006, 36, 679
O
H MeOH, reflux, 15 min
O
OH
87%
H2O2 (4 equiv)KOH (3 equiv)
O
H
O OH
HO O
H
K+ MeOH
O OH
K
+
O
H
O OH
H OMeK
H OMeK+ OH–
OMeK + H2O
OMeK
HO
H
O OH
OMeK
O
OH
HOMe
KOH
+
+
O
O OMeK
K
HOMe+
workupO
OH
3
Part II.
Lautens, M.; Colucci, J. T.; Hiebert, S.; Smith, N. D.; Couchain, G. Org. Lett. 2002, 4, 1879.
EtO
O O
OEt+
1 equiv 1 equiv
NaOEt (1 equiv)
EtOH, reflux, 2 h
O
OEtEtO
O
O
EtO
77%
O
OEtBr
O
OEtBr
H
EtO
O O
OEt
NaOEt
H
EtO
O O
OEt
+ EtOH
Na
NaOEt
O
OEt+ NaBr + EtOH
EtO
O O
OEt
O
OEt+
O
OEtEtO
O
O
EtO
Na
Na EtO
O O
OEtH
O
OEtEtO
O
O
EtO
EtO
O O
OEt
Na
+
4
2) Propose a mechanism for the following reaction (10 pts)
Gonzalez, M.; Gandara, Z.; Covelo, B.; Gomez, G.; Fall, Y. Tetrahedron Lett. 2011, 52, 5983.
OOTBDPS
oxygenRose Bengal (3 mol%)
MeOH, –78 °C, 3 hphotolysis
i-Pr2NEt (4.2 equiv)O
OTBDPSO
OH
≥ 71%
O
O O O Ophotolysis
Rose bengal
O O
OO
OTBDPS
OTBDPS
OOO OTBDPS
H
i-Pr2NEt
O
i-PrN Et
Hi-Pr
OOTBDPS
OOH
i-Pr2NEt+
5
3) Propose a mechanism for the following reaction (10 pts).
Frost, J. R.; Pearson, C. M.; Snaddon, T. N.; Booth, R. A.; Ley, S. V. Angew. Chem. Int. Ed. 2012, 51, 9366.
Me3Si
OOTBS OMe
Me3Si
OHOTBS
89%
+ CH2Cl2, 0 °C, 80 min
pH 7 buffer
1.9 equiv
O
O
CN
CNCl
Cl
O
O
CN
CNCl
ClMe3Si
OOTBS OMe
+electrontransfer
O
O
CN
CNCl
Cl
Me3Si
OOTBS O
+
MeH O H
O
O
CN
CNCl
Cl
Me3Si
OOTBS
+
OMeO H
H
OH
O
CN
CNCl
Cl
Me3Si
OOTBS
+
OMeO H
electrontransfer
OH
O
CN
CNCl
Cl
Me3Si
OOTBS
+
OMeO H
H
OH
OH
CN
CNCl
Cl
Me3Si
OOTBS
+
OMeOH
H O H
HMe3Si
OOTBS
OMeOH
H Me3Si
OOTBS
H2O+
OMe
H2O+
Me3Si
OOTBS OMe
O HH
H O HMe3Si
OOTBS OMe
OH
H O H
H+
Me3Si
OTBSO OMe
OHH2O+
H
Me3Si
OHOTBS
H
O
OMe
H
+ H O HH
O
OMeH O H
H+
6
4) Propose a mechanism for the following reaction (15 pts).
Dissanayake, A. A.; Staples, R. J.; Odom, A. L. Adv. Synth. Catal. 2014, 356, 1811.
N
C
NH
N86%
CNNC2 equiv
DBU (0.5 equiv)
ethanol, 80 °C, 2 hmolecular sieves
N
NDBU
N
C
HN
N
N
C
HN
N
N
C
NH
N
CNNC
H H
N
C
N
N
+
CNNC
H
H
N
N
+
NN NH2
C N
N
NN NH2
C N
N
electrocyclicring opening
H2NN N
C N
N
NN N
C N
NHH N
C
N
N
H
N
N
+
H
N
N
H
N
C
N
N
H
+
N
N
N
C
N
N
H
+
H
+
N
NH
CNNC
N
NCNNC+
7
5) Propose a mechanism for the following reaction (10 pts).
O
O N
O
O N
H
O
H
H
45%
+DMF, rt, 24 h
1.5 equiv 1.0 equiv
OSiMe3
I
O
O N
OSiMe3
I+
O
O N
OSiMe3
I
O
O N
O
H
HMe3Si
IO
O N
H
O
H
H
Me3SiI+
8
6) Propose a mechanism for the following reaction (10 pts).
Prasad, P. K.; Reddi, R. N.; Sudalai, A. Org. Lett. 2016, 18, 500.
DBU (1 equiv)NBS (1 equiv)
Me2SO, rt, 8 h
ON
O
O
86%
N
O
O
Br
NBS
N
NDBU
N
O
O
Br
SO
+N
O
O
SO
+
Br
SOBr Br
+ BrO
S
H
N
N
OBr
+ Me2SN
NH
+O
N
O
O
N
O
O
SO
N
NH
+
Br
9
7) Propose a mechanism for the following reaction (10 pts).
Liu, Y.; Huang, C.; Liu, B., Tetrahedron Lett. 2011, 52, 5802.
OH
OH
OAc
AcOOH toluene, rt
O
HOOAc
OAc
86%
SO3H
OH
OH
OAc
AcOO H
SO3
OH
OH
OAc
AcOO H
H
OH
OH
OAc
O
+ H2O
O
OH
OH
OAc
OO
OH
HOOAc
OAc
SO3
SO3H
O
HOOAc
OAc
SO3H+
SN1O
HOOAc
OAc
H
10
8) Propose a mechanism for the following reaction (15 pts).
Part I
Stetter, H.; Ramsch, R. Y.; Kuhlman, H. Synthesis, 1976, 733.
O
H EtOH, 80 °C, 1.5 h
catalyst (5 mol%) O
OH
94%
Et3N (0.33 equiv)
Br
catalyst
SN
OH
SN
OH
Br HNEt3 SN
OHHNEt3 Br+
O
HSN
OH
+
O
H N
SHNEt3 BrOH
HO
H N
SOH
Br
NEt3+
HO
N
SOH
HNEt3 Br+
O
HO
N
SOH
OH
O
N
SOH
HO
O
OH
SN
OH
+
11
Part II
O
H EtOH/H2O (1.3:1), reflux, 30 min
KCN (16 mol%)O
OH
Adams, R.; Marvel, C. S. Org. Synth. 1921, 1, 33.
91-92%
O
H K+ CN–O
HCN
K
H OEtHO
H
CN
K OEt
HO CN
+ HOEt
O
H
HO
O
CNH OEt
O
OH
CN
K
KK OEt
H O
OH
CN
+ HOEt
K O
OH
+ KCN
12
9) Propose a mechanism for the following reaction (10 pts).
Lambert, T. H.; MacMillan, D. W. C. J. Am. Chem. Soc. 2002, 124, 13646.
Me N+ Zn(OTf)2 (5 mol%)
CH2Cl2, rt, 2 h
93%2 equiv
C CMe
COBn
O
Me
Me
N
O OBn
C CMe
COBn
O
Me
Me
N
BnO O
Zn(OTf)2 C CMe
COBn
OZn(OTf)2
Me NMe N
OBn
O Zn(OTf)2
Me
Me NOBn
O Zn(OTf)2
Me
aza-Claisen
Zn(OTf)2
Me
Me
N
O OBn
Zn(OTf)2+
N
BnO
(OTf)2ZnO
chair transition state gives syn product
13
10) Propose a mechanism for the following reaction (15 pts).
Stork, G.; Sher, P. M. J. Am. Chem. Soc. 1986, 108, 303.
O O
I
H OH
H
O
CN
60%
t-BuOH, reflux, 4 h
NaCNBH3 (2 equiv)n-Bu3SnCl (0.1 equiv)
AIBN (10 mol%)+
20 equiv
The purpose of NaCNBH3 is to reduce n-Bu3SnX to n-Bu3SnH
N CNNNC
AIBN
NC
NC
N NCN
NC heat+ CNN N 2
H BH2CN
n-Bu3Sn H
Nan-Bu3Sn X + NaXn-Bu3Sn H
n-Bu3SnCN
H
+
+
O O
I
Hn-Bu3Sn O OH
+ n-Bu3Sn I
OH
H
O
OH
H
O
CN
OH
H
O
CN
+
n-Bu3Sn H CN+
n-Bu3Sn H+
X = Cl, I
14
11) Propose a mechanism for the following reaction (10 pts).
Chen, Z.-H.; Tu, Y.-Q.; Zhang, S.-Y.; Zhang, F.-M. Org. Lett. 2011, 13, 724.
OMe
OMe
N3Me3SiO
H
N
H
O
OMe
82%dr = 1:0.84
CH2Cl2, –78 °C, 15 min;10 °C, 3 h
TiCl4 (2.2 equiv)
OMe
OMe
N3Me3SiO
H
TiCl4
OMe
N3Me3SiO
H
MeOTiCl4
OMe
N3
H
Me3SiO
MeOTiCl4
OMe
H
OMe3Si
MeOTiCl4
NN
N
NO
NN
Me3Si
H
OMe
MeOTiCl4
N
H
O
OMeN
H
O
OMe
Me3Si
MeOTiCl4
N N+
+ Me3SiOMe
+ TiCl4
15
12) Propose a mechanism for the following reaction (10 pts).
Guthbertson, J. D.; Godfrey, A. A.; Taylor, R. J. K. Org. Lett. 2011, 13, 3976.
O O
N
Me
HH NO
N
H
H
Me
72%
30% aq NH3
0 °C to rt, 2 h
16
13) Propose a mechanism for the following reaction (10 pts).
Vecchione, M. K.; Sun, A. X.; Seidel, D. Chem. Sci. 2011, 2, 2178.
H
O
NH2NH
+
1.1 equiv 1.0 equiv
SO3H
1 equiv
toluene, reflux, 30 minN NH2
83%
H
O
NH2
+ SO3 H H
O
NH2
H
SO3
+
NH
+
NH
OHNH2
H
SO3
NH
OHNH2
+ SO3 H
NH
OH2NH2
SO3
+
NH
+ H2O
NH2 N NH
HH
SO3
NH
NH
SO3 H
NH
N HH
SO3
+ +
N NH2
H
SO3
N NH2
SO3 H
+
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