Type III Intramolecular Cycloadditions of Vinylketenes

Article abstract of DOI:10.1021/jo00257a022

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 30-50percent yield from the acid chloride.The effect of substituents on the stereochemistry and regiochemistry of the cycloaddition is described.