Photochemical reactions between benzoquinones and alkylidenecyclohexanes proceed regioselectively. Regioselectivity is determined by the conformational properties of the cyclic olefin. Photocycloadducts thus obtained may be used for the construction of important alkaloidal frameworks in synthetically useful yields. Oxetane formation is likely to occur through concerted collapse of an exciplex that possesses considerable charge transfer character.