Site-selective intramolecular (2π+2π) photocycloaddition of trans-2-butenyl 1-cyano-2-naphthylmethyl ether depending on the polarity of the solvent

Irradiation of trans-2-butenyl 1-cyano-2-naphthylmethyl ether 1b afforded two kinds of intramolecular (2π+2π) photocycloadducts at the 1,2- and 3,4-positions in a stereoselective manner. The product ratio was dependent on the solvent polarity based on the nature of the exciplex.