Irradiation of 2,3-dimethylbut-2-enyl 1-cyano-2-naphthylmethyl ether in the presence of Eu(hfc)3 in benzene site-selectively afforded the (2Ï + 2Ï) intramolecular photocycloadduct at the 1,2-position on the naphthalene ring. On the other hand, allyl 1-cyano-2-naphthylmethyl ether in the presence of Mg(ClO4)2 in acetonitrile gave the photocycloadduct at the 3,4-position as a sole product.
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.