The ring expansion of α-cyclopropyl diazoacetates into cyclobutenoates upon irradiation at 425 nm was reported in moderate to excellent yields (17% to 75%) and moderate to good regioisomeric ratio (55:45 to 82:18). The formation of two regioisomers was explained using DFT calculations as well as the involvement of a singlet state carbene.

Abstract

The ring expansion of α-cyclopropyl diazoacetates into cyclobutenoates upon irradiation at 425 nm was reported. This method allowed an access to a large array of cyclobutenoates as a mixture of regioisomers. The products were isolated in moderate to excellent yields (17% to 75%) and moderate to good regioisomeric ratio (55:45 to 82:18). The synthetic utility of the products was showcased and the mechanism was studied. Thanks to DFT calculations, the formation of two regioisomers was explained as well as the involvement of a singlet state carbene.