Photochemical syntheses. VII. The formation of 1,2-Diaryl-8b-methoxy-2a,8b-dihydrocyclobuta[a]naphthalenes in photoadditions involving 1-methoxy-naphthalene and heterocyclic diarylacetylenes

Abstract

The diarylacetylenes (2), (3), (4), (9, (6), and (7) react with 1- methoxynaphthalene on ultraviolet irradiation to give 1,2-diaryl-8b- methoxy-2a,8b-dihydrocyclobuta[a]-naphthalenes (d) and/or (d?). Phenyl(4-pyridyl)acetylene (2), phenyl(3-pyridyl)-acetylene (3), di(3- pyridyl)acetylene (5) and phenyl(2-furyl)acetylene (6) also give tetracyclic photoadducts (c) and/or (c?). The major product of the reaction with (2) is a benzo[h]isoquinoline which is formed by photodehydrocyclization of (2d) and for which structure (2f) is proposed on spectral grounds. Similarly (3) gives a benzo[f]-quinoline (3g) and two benzo[h]quinolines (3h) and (3h?).     Thermolysis of (3c) and (3c?) gives (3e) and (3e?), respectively. These isomerizations are quantitatively reversed by ultraviolet irradiation but irradiation of (3d) and (3d?) gives mixtures containing (3h), (3h?), (3c), and (3c?). Di(3-pyridyl)acetylene (5) forms with naphthalene the photoadduct (5a).