Synthesis of 6-phenylbenzo[h]quinolines via photoinduced dehydrogenative annulation of (E)-2-phenyl-3-styrylpyridines

A concise and environmentally friendly protocol was developed for the synthesis of 6-phenylbenzo[h]quinolines. 6-Phenylbenzo[h]quinolines were obtained in good yields via irradiation of (E)-2-phenyl-3-styrylpyridines with a 254 nm UV light (64 W) in EtOH under an argon atmosphere in the presence of TFA. The reaction is a dehydrogenative annulation reaction that proceeds through 6 pi-electrocyclization, a [1,5]-H shift, 1,3-enamine tautomerization, and elimination of a hydrogen molecule to afford 6-phenylbenzo[h]quinolines. The described protocol not only avoids the usage of a transition metal catalyst and an oxidant but also has the advantages of high atom efficiency and mild reaction conditions.

Automated summary

The method utilizes UV irradiation to achieve the synthesis of 6-phenylbenzo[h]quinolines without the need for transition metal catalyst and oxidant, offering high atom efficiency and mild reaction conditions.