Paternó-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 PaternoeB€uchi 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.