Page 567 - Advanced Organic Chemistry Part A - Structure and Mechanisms, 5th ed (2007) - Carey _ Sundberg

548 Scheme 5.2. Representative -Elimination Reactions

CHAPTER 5 A. Dehydrohalogenation
+–
Polar Addition 1 a CH 3 (CH 2 ) 15 CH 2 CH 2 Br K OC(CH 3 ) 3 CH 3 (CH 2 ) 15 CH CH 2
and Elimination (CH 3 ) 3 COH 85%
+–
Reactions Na OCH 3
2 b CH 3 (CH 2 ) 2 CH 2 CHCH 3 CH 3 (CH 2 ) 4 CH CH 2 + CH 3 CH 2 CH 2 CH CHCH 3
Br CH 3 OH 19% 55% ; E:Z = 3.6
+ CH 3 (CH 2 ) 2 CH 2 CHCH 3
26%
OCH 3
+–
K OC(c–C 5 H 9 ) 3
CH 3
3 c CH 2 + CH 3
Cl
75:25
DBU
4 d (CH 3 ) 2 CHC(CH 3 ) 2 (CH 3 ) 2 C C(CH 3 ) 2 + (CH 3 ) 2 CHC CH 2
Br
92:8 CH 3
O O
NaOAc
5 e PhCHCHCCH 3 PhCH CCCH 3
Br Br Br
64–73%
B. Dehydrosulfonation
Na + – OCH 3
6 f Ph 2 CHCH 2 OSO 2 C 7 H 7 Ph 2 C CH 2
92%
+–
K OC(CH 3 ) 3
7 g OSO 2 C 7 H 7 76%
C. Eliminations of Quaternary Ammonium Hydroxides
+
8 h (CH 3 ) 3 CCH 2 CH 2 N (CH 3 ) 3 – OH heat (CH 3 ) 3 CCH CH 2
81%
heat CH 3
9 i CH 3 C(CH 3 ) 2 – OH CH 3
H 2 O
+ CH 2
N (CH 3 ) 3 98%
a. P. Veeragu, R. T. Arnold, and E. W. Eigemann, J. Am. Chem. Soc., 86, 3072 (1964).
b. R. A. Bartsch and J. F. Bunnett, J. Am. Chem. Soc., 90, 408 (1968).
c. S. A. Acharya and H. C. Brown, J. Chem. Soc., Chem. Commun., 305 (1968).
d. P. Wolkoff, J. Org. Chem., 47, 1944 (1982).
e. N. H. Cromwell, D. J. Cram, and C. E. Harris, Org. Synth., III, 125 (1953).
f. P. J. Hamrick, Jr., and C. R. Hauser, J. Org. Chem., 26, 4199 (1961).
g. C. H. Snyder and A. R. Soto, J. Org. Chem., 29, 742 (1964).
h. A. C. Cope and D. L. Ross, J. Am. Chem. Soc., 83, 3854 (1961).
i. L. C. King, L. A. Subluskey, and E. W. Stern, J. Org. Chem., 21, 1232 (1956).
5.10.1. The E2, E1 and E1cb Mechanisms

The ß-eliminations can be subdivided on the basis of the mechanisms involved.
Three distinct limiting mechanisms are outlined below.

E2 Mechanism (concerted)
B: – B
H H H H R
R C C R R RCH CHR
H X
H X