Photo-additions of Naphthalene Derivatives with Substituted Ethylenes: Influence of Methoxy- and Cyano-substituents on the Products

Irradiation of 2-methoxynaphthalene and acrylonitrile in ethanol affords exo- and endo-7-cyano-6-methoxy-2,3-benzobicyclo[4.2.0]octa-2,4-diene, in the ratio 30:70. The structures are assigned from the n.m.r. spectra. The endo compound is the more stable, and on base equilibration predominates (90%). These adducts eliminate a methoxy-group on treatment with tert-butoxide at 80°, to afford 2,3-naphtho-cyclobutene carboxamide. Irradiation of 2-cyanonaphthalene and methyl vinyl ether in ethanol gives a complicated mixture of adducts which includes the cyclobutane 7-methoxy-6-cyano-2,3-benzobicyclo-[4.2.0]octa-2,4-diene as a major product (35%). Also formed are 7-methoxy-2,3(8-cyanobenzo)bicyclo-[3.3.0]octa-2,7-diene (8%), 8-methoxy-10-cyano-1,2-benzocycloocta-1,3,5-triene (18%), and a dimer of the latter (7%), and 8-methylene-5-methoxy-2,3(10-cyanobenzo)bicyclo[2.2.1]heptene (35%). The structures of the latter adducts are assigned from spectroscopic data, including nuclear Overhauser effects. Possible mechanisms for formation of the latter adducts, and a rule for prediction of regiospecificity in cyclobutane formation, are proposed.