Photochemical conversion of 2,6-dihalo substituted methyl alpha-phenylcinnamates

Photolysis of methyl alpha -phenylcinnamate derivatives which have both ort ho positions of the beta -aromatic ring halogenated gives methyl 9-phenanth roates as the only identifiable products in good yields. This photochemical conversion involves a photocyclization with subsequent dehydrohalogenation , and is insensitive to oxygen. The mechanism of this transformation is bri efly discussed: electronic factors seem to govern the outcome of the reacti on but steric factors are apparently also of importance. The ester group at tached to the double bond seems to be essential for the cyclization to take place. (C) 2001 Elsevier Science B.V. All rights reserved.