Photo-dehydro-Diels–Alder reaction of 1-phenyl-2-(pyridyl)acetylenes in acidic aqueous solution

The photocycloaddition of 1-(4-R-phenyl)-2-(4-pyridyl)acetylenes (R = H, Br, CH3, Cl) and 1-(4-R-phenyl)-2-(2-pyridyl)acetylenes (R = H, Br, Cl) was carried out in acidic aqueous solution. The unexpected photo-dehydro-Diels–Alder reaction of these monomers was observed, and the results show that two monomers react in a head-to-tail manner and lead to the formation of 2-phenyl-1,3-di(pyridyl)naphthalene derivatives. This reaction presents a direct metal-free method to construct the 1,2,3-triaryl substituted naphthalenes from diarylacetylenes.