Accessing oxy-functionalized N-heterocycles through rose bengal and TBHP integrated photoredox C(sp3)–O cross-coupling

Abstract

Herein, we report a practical and simple mono- and di-C(sp³)–O cross-coupling of tautomerizable N-heterocycles (dihydrophthalazine-1,4-diones, pyridone, quinoxalinone and pyrimidinone) with ketones, β-dicarbonyl compounds and nitroalkane, leading to substituted imidate derivatives under visible-light conditions. The combination of rose bengal as the photocatalyst and TBHP enables sustainable reaction conditions, operational simplicity, and high chemo- and regioselectivity with exceptional yields (up to 94%), good functional group tolerance and substrate generality. In the case of unsymmetrical ketones, the less substituted end is functionalized selectively. The di-C–O coupling products are generally obtained with ketones containing three enolizable ‘H’ at the reaction site while ketones with two enolizable ‘H’ furnished only single coupling products. Radical inhibition experiments revealed the involvement of a radical pathway in this coupling strategy. The coupling products are also scaled up to the gram scale, offering scope for further functionalizations via C–H bond activation.