Synthesis of Cyclobutenoates From Photochemical Rearrangement of α‐Diazo Cyclopropanes and Computational Studies

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.