Page 706 - Advanced Organic Chemistry Part B - Reactions & Synthesis

682 3-Acetoxy-2-methyl-1-alkenes react primarily at C(1), owing to steric factors. 29

CHAPTER 8 CH 3
CH 3
Reactions Involving R (CH ) CuLi CH 3 R
3 2
Transition Metals CH 2
O CCH 3
2
5-Acetoxy-1,3-alkadienes give mainly -alkylation with dialkylcopper-magnesium
reagents. 30

O CCH 3
2
CuI
+ CH (CH ) MgBr H
C H 3 2 3 C 7 15 C H
4 9
7 15
10:1E,E:Z,E 83%
High -selectivity has been observed for allylic diphenyl phosphate esters. 29
O
CuCN, 2 LiCl C H
7 15
C H OP(OPh) 2 + CH (CH ) MgCl
7 15
3
2 3
o
H
–76 C C 4 9
98%
The reaction of cyclic allylic acetates shows a preference for anti stereochem-
istry. 31
CH 3 CH 3
[Me Cu]Li
2
O CCH 3 CH 3
2
The preferred stereoelectronic arrangement is perpendicular alignment of the acetate
with respect to the double bond. For example, the cis and trans isomers of 1-vinyl-2-
methylcyclohexyl acetate show divergent stereochemical results. Only the exocyclic
E-isomer is formed from the cis compound, whereas the trans compound gives a 1:1
mixture of the E- and Z-isomers. This is the result of a strongly preferred conformation
for the cis isomer, as opposed to a mixture of conformations for the trans isomer. 32

O 2 CCH 3 O CCH O CCH 3
2
O 2 CCH 3 2 3

(CH ) CuLi (CH ) CuLi CH 3
3 2
3 2
+
CH 3
CH 3 76% only 79% 1:1 mixture
isomer

29 R. J. Anderson, C. A. Hendrick, and J. B. Siddall, J. Am. Chem. Soc., 92, 735 (1970).
30
N. Nakanishi, S. Matsubara, K. Utimoto, S. Kozima, and R. Yamaguchi, J. Org. Chem., 56, 3278
(1991).
31 H. L. Goering and V. D. Singleton, Jr., J. Am. Chem. Soc., 98, 7854 (1976); H. L. Goering and
C. C. Tseng, J. Org. Chem., 48, 3986 (1983).
32
P. Crabbe, J. M. Dollat, J. Gallina, J. L. Luche, E. Velarde, M. L. Maddox, and L. Tokes, J. Chem.
Soc., Perkin Trans. 1, 730 (1978).