Hantzsch Ester-Mediated Benzannulation of Diazo Compounds under Visible Light Irradiation.

A metal-free benzannulation of diazo compounds under visible light irradiation was developed. The photocatalytic single electron transfer by Hantzsch ester to the diazo enolates results into enolate vinyl radicals, which were trapped by alkynes leading to functionalized naphthalene-1-ols. The enolate vinyl radicals were also trapped intramolecularly by -aryl groups to access phenanthren-10-ols. The wide substrate scope and mild conditions employing inexpensive Hantzsch ester as photosensitizer are noteworthy attributes of the reaction.