Photochemical syntheses. V. The photo-addition of heterocyclic diarylacetylenes to naphthalene and 1-methylnaphthalene

Eight heterocyclic diarylacetylenes derived from pyridine, furan, thiophen, and thiazole have been irradiated in the presence of naphthalene. Phenyl(4-pyridyl)- acetylene gave the compounds (2a) and (2b), phenyl(3-pyridyl)acetylene gave the compounds (3a) and (3b), and phenyl(2-pyridyl)acetylene compounds (4a) and (4b). From 1-methylnaphthalene and phenyl(3-pyridyl)acetylene the adducts (5a) and (5b) have been isolated and two adducts which formed by addition to the unsubstituted ring were detected. From phenyl(2-thiazolyl)acetylene and naphthalene probably only one isomeric adduct (6b) was isolated. The methiodides of all the new adducts except (6b) have been prepared. The structures proposed for these photo-adducts are based on their p.m.r., mass, and ultraviolet absorption spectra. Factors influencing the isomer distribution and overall yields are discussed in terms of a mechanism previously proposed for the addition of diphenylacetylene to naphthalene.