LOW-TEMPERATURE IRRADIATION OF 1-SUBSTITUTED NAPHTHALENES

An unprecedented photodimerization of 1-substituted naphthalenes is re ported, Upon irradiation of naphthalene-1-carbonitrile or methyl 1-nap hthoate through a Pyrex filter at -78 degrees C, the corresponding syn -[2+2] cyclodimer was isolated as a single product. However, no cyclod imer was found in the irradiation of 1-methylnaphthalene, 1-methoxynap hthalene, and naphthalene under the same irradiation conditions. By a tripler-sensitized photoreaction and low-temperature NMR study of the reaction mixture irradiated at low temperature, the syn-[2+2] cyclodim er was found to be produced through a facile Cope rearrangement of the exo-[4+4] cyclodimer which was the primary product formed by a single t-state 1,4-4',1' dimerization of the substituted rings.