photoproducts. Chemoselectivity of the photocycloaddition of BCP with naphthoquinones relies largely on the substitution groups linked to the C═C in between the two carbonyl groups to give different types of products. Photoreaction of BCP with 9,10-anthraquinone gave not only the spirooxetane product, but also a novel spiro[indan-1,1′-phthalan]-3′-one product whose formation might be initiated by a transannular