Page 1192 - Advanced Organic Chemistry Part B - Reactions & Synthesis

1168 O O O
H
OC 2 5
CHAPTER 13 (CH 2 C) CuLi + CH 3 CH 3 H + CH
2
Multistep Syntheses CH 3 CH 2 C CH 3 H O CH C CH 3 3
2
3
H 67% 74%
OC 2 5 O
Ref. 8
9
Lithiation of vinyl thioethers and vinyl carbamates 10 also provides acyl anion equiv-
alents.
Sulfur compounds are useful as nucleophilic acyl equivalents. The most common
reagents of this type are 1,3-dithianes, which on lithiation provide a nucleophilic
acyl equivalent. In dithianes an umpolung is achieved on the basis of the carbanion-
stabilizing ability of the sulfur substituents. The lithio derivative is a reactive nucleo-
phile toward alkyl halides and carbonyl compounds. 11

S S 2+ HO
CH 3 n-BuLi CH 3 O S HO Hg
S S Li H O, CaCO 3 CH 3 C
2
S CH 3
O
1,3-Dithianes have found considerable application in multistep syntheses. 12
Scheme 13.1 summarizes some examples of synthetic sequences that employ acyl
anion equivalents.

Scheme 13.1. Synthetic Sequences Using Acyl Anion Equivalents
Li
1 a OEE + O
LDA R′X H
RCHCN RCCN RCR′ RCR′
H O
OEE OEE CN 2 O
2 b OC H
2 5
Br CH Br Br CH CCH 3
2
2
+ – Cu(CH CH 2 2
)
(CH ) CH H (CH ) CH H
3 2
3 2
O
3 c S S RR′X S R Hg 2+
R n-BuLi RCR′
S S Li S R′ H O
2
O
4 d s-BuLi R′I HgCl 2
H
C CHSC H CSC H
R 2 2 5 R C CSC 2 5 R C 2 5 R CHCR′
2
2
2
H O
2
Li R′ SPh O
5 e
+
Li Naphth – R′CH O
C C CSPh C CCHR′ R CHCCHR′
R 2 C(SPh) 2 R 2 R 2 2
Li OH OH
a. G. Stork and L. Maldonado, J. Am. Chem. Soc., 93, 5236 (1971).
b. P. Canonne, R. Boulanger, and P. Angers, Tetrahedron Lett., 32, 5861 (1991).
c. D. Seebach and E. J. Corey, J. Org. Chem., 40, 231 (1975).
d. K. Oshima, K. Shimoji, H. Takahashi, H. Yamamoto, and H. Nozaki, J. Am. Chem. Soc., 95, 2694 (1973).
e. T. Cohen and R. B. Weisenfeld, J. Org. Chem., 44, 3601 (1979).
9 K. Oshima, K. Shimoji, H. Takahashi, and H. Nozaki, J. Am. Chem. Soc., 95, 2694 (1973).
10
S. Sengupta and V. Sniekus, J. Org. Chem., 55, 5680 (1990).
11 D. Seebach and E. J. Corey, J. Org. Chem., 40, 231 (1975); B. H. Lipshutz and E. Garcia, Tetrahedron
Lett., 31, 7261 (1990).
12
M. Yus, C. Najera, and F. Foubelo, Tetrahedron, 59, 6147 (2003); A. B. Smith, III, and C. M. Adams,
Acc. Chem. Res., 37, 365 (2004).