Photolysis of 4-methoxyphenyl aryl alkylphosphonates

UV irradiation of bis(4-methoxyphenyl) methylphosphonate 1a in methanol gave 4,4'-dimethoxybiphenyl 2a as the main product through an intramolecular excimer. With 4-cyanophenyl-4-methoxyphenyl methylphosphonate 1b 4-cyano-4'-methoxybiphenyl 2c and 4-cyano-2-(4'-methoxyphenyl)phenyl methylphosphonate 4b were obtained through an intramolecular exciplex. 3-cyanophenyl-4'-methoxyphenyl methylphosphonate 1c gave only 3-cyano-4'-methoxybiphenyl 2f. Methyl 4-methoxyphenyl 4-chlorobenzylphosphonate 5a gave methyl 4-chlorobenzyl-2-(4'-methoxyphenyl)phosphonate and methyl 2-(4'-methoxyphenyl)benzylphosphonate.