Abstract
Treatment of trans ,ß-unsaturated acid chlorides with EtaN in benzene at reflux gives a ca. 1:1 mixture of
cis and trans ,/3-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.