Paternò–Büchi reaction versus hydrogen abstraction in the photochemical reactivity of alkenyl boronates with benzophenone

The photochemical reaction between some alkenyl boronates and benzophenone is described. While a pinacol alkenyl boronate derivative gave the corresponding oxetane, the MIDA esters gave a tertiary alcohol derived from allylic hydrogen abstraction by triplet benzophenone and coupling of the radicals thus obtained. A theoretical work at DFT level of theory performed on a MIDA ester explained this behaviour showing that the formation of the tertiary alcohol is the most probable reaction. Furthermore, the theoretical calculations showed that the Paternò–Büchi reaction occurs giving the C,C biradical intermediate and this result is not in agreement with the previous described hypothesis where electron poor alkenes gave mainly the C,O biradical intermediate.