Photochemistry of butyrophenone and its α-substituted derivative: a theoretical examination of a new photochemical route to cyclopropane group formation

Abstract

The potential energy surfaces of dissociations and isomerizations for butyrophenone and its α-substituted derivative in low-lying electronic states have been studied with use of the CASSCF and DFT methods. A three-surface (S1, T1 and T2) intersection was found in the present work and this plays an important role in the S1 → T1 process for butyrophenone and related aromatic carbonyl compounds. Examination of these results provides some new insights into the mechanistic photochemistry of aromatic ketones. The most probable mechanism leading to formation of a cyclopropane moiety was obtained on the basis of the calculated potential energy surfaces and their intersections. The selection of a suitable α-substituent was found to be a key step for cyclopropanation to occur by photoexcitation of butyrophenone derivatives.