Photolytic studies of cyclic unsaturated ketones. I. Irradiation products of 2-Methylcyclobutane-1,3-dione and its ethyl enol ether

Abstract

The photochemical rearrangement of 2-methylcyclobutane-1,3-dione and the ethyl ether of its enol (4) have been shown to follow the expected pathway for an α, β-unsaturated cyclobutenone. The enol ether, when irradiated in moist cyclohexane, forms 3-ethoxy-2-methyl-trans-crotonic acid (8) which is photo-isomerized to the cis-isomer (7). This latter isomer is the major product when the solvent is moist diethyl ether. It is suggested that the necessary rotation about a carbon-carbon single bond is solvent-dependent, and occurs in a β,γ-unsaturated carboxylic acid formed as a reaction intermediate.