Reactions of sulfur-containing carbanions with ethyl 4-bromocrotonate. A facile synthesis of cyclopropanecarboxylates

✍ Scribed by E. Ghera; Y. Ben-David

• Book ID: 104237998
• Publisher: Elsevier Science
• Year: 1979
• Tongue: French
• Weight: 223 KB
• Volume: 20
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)86661-2

✦ Synopsis

Ethyl 4-bromocrotonate reacts as a Michael acceptor with carbanions derived from phenylsulfones and B-ester sulfides; the conjugated addition is followed by the displacement of Br-affording various cyclopropanecarboxylates.

In reactions of sulfur-containing carbanions with a,B-unsaturated y-bromoesters, the possibility of two processes can be envisaged: a) alkylation by a nucleophilic substitution reaction and b) an initial Michael addition of the carbanions to the a,B-unsaturated ester.

Alkylation reactions of sulfur-containing carbanions by displacement on ally1 halides occur readily' and an a-sulfonyl carbanion has been shown to react in this manner with an unsaturated bromoester.

2 Specifically, previously reported reactions of carbonyl-derived carbanions with ethyl 4-bromocrotonate occurred by way of nucleophilic substitution. 3

' H NMR (270 MHz, CDC13) 6 1.06, (3H, t, J=7 Hz), 1.25 (3H, t, J=7 Hz), 2.49 (t, ZH, J=7 Hz, when hv at 2.81, collapses to s), 2.81 (dt overlapped to q, J=7 Hz, when hv at 7.32, collapses to t), 4.09 (dq, 4H, J=7 Hz), 7.09-7.26 (m, 5H) and 7.32 (t, lH, J=7 Hz); l3 C NMR (CDC13) 6 172 and 165; IR (film):vCO 1718 and 1731 cm -1

This conversion, which occurs probably by proton abstraction from 6a followed by ring'opening to 8, represents an interesting and novel intramolecular nucleophilic cleavage of a monoactivated cyclopropane which is not part of a strained ring system.