Type III Intramolecular [2 + 2] Cycloadditions of Vinylketenes

Abstract

Treatment of trans α,β-unsaturated acid chlorides with Et3N in benzene at reflux gives a ca. 1:1 mixture of cis and trans α,β-unsaturated ketenes in excellent yield. If there is a second double bond in the side chain, the cis isomer undergoes a type III intramolecular cycloaddition to produce a bicyclo[3.2.0]hept-3-en-6-one and/or a bicyclo[3.1.1]hept-2-en-6-one in 30–50% yield from the acid chloride. The effect of substituents on the stereochemistry and regiochemistry of the cycloaddition is described. © 1988, American Chemical Society. All rights reserved.