NH4OAc-Promoted Cascade Approach towards Aberrant Synthesis of Chromene-Fused Quinolinones

A concise cascade strategy for the synthesis of 6H-chromeno[4,3-b]quinolin-6-ones was developed from 4-hydroxycoumarins and arylhydrazine hydrochlorides in DMSO. The synthetic strategy relies on dual role of ammonium acetate in generating 4-aminophenyl coumarin from arylhydrazine via aryl radical formation, and Csp(2)-H formylation of coumarin using DMSO as a methine source. The strategy is scalable, and an array of arylhydrazine hydrochlorides delivered chromene-fused quinolinones in good to excellent yields.