Photo-promoted radical cascade cyclization of 4-(allylamino)-3-cyanocoumarins: access to sulfonylated pyrido[3,2-c]coumarin derivatives†

Abstract

We present the first method for constructing pyrido[3,2-c]coumarin derivatives via a radical cascade cyclization process that enables the introduction of active fragments into these frameworks. In this approach, we design and synthesize a new category of precursor skeletons, specifically 4-(allylamino)-3-cyanocoumarins. Meanwhile, a mild photo-induced multicomponent reaction (MCR) is proposed, which can initiate the radical sulfonylation and cascade cyclization of these precursors, thereby affording a broad range of sulfonylated pyrido[3,2-c]coumarin derivatives in a green and efficient manner. Notably, the method obviates the use of any metal catalyst and additive, showing good functional group tolerance and substrate scope. Furthermore, gram-scale reactions and subsequent derivatizations proceed smoothly, underscoring the practicality and scalability of our methodology.