Photocycloaddition of some difluoro(aminoenonato)boron complexes with arylalkenes

The photocycloaddition of some difluoro[(methylamino-kappaN)alkenonato-kappaO]boron complexes 1 with arylalkenes 2 is discussed. The resulting [2 + 2] photoaddition gave the cyclobutane and azetidine derivatives (Schemes 1, 3, and 5). Rearrangements of the cyclobutane gave 1,5-diketones derivatives (Schemes 2, 4, and 5). The yields of the photoadducts were governed by the reduction and oxidation potentials. Furthermore, the configurations of the products established high regio- and stereoselectivity, suggesting the presence of a singlet exciplex. The reactivity and the stereochemistry were rationalized by means of FMO (frontier molecular orbital) calculations.