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

• The photocycloaddition of 1-phenyl-2-(pyridyl)acetylenes in acidic aqueous solution is a typical photo-dehydro-Diels–Alder reaction.
• This photoreaction presents a direct metal-free method to construct 1,2,3-triaryl substituted naphthalenes from diarylacetylenes with mild conditions.
• The 1,2,3-triaryl substituted naphthalene is formed in a head-to-tail manner.

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.

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