Flow photolysis of aryldiazoacetates leading to dihydrobenzofurans via intramolecular C–H insertion

Abstract

Flow photolysis of aryldiazoacetates 3–5 leads to C–H insertion to form dihydrobenzofurans 6–8 in a metal-free process, using either a medium pressure mercury lamp (250–390 nm) or LEDs (365 nm or 450 nm) with comparable synthetic outcomes. Significantly, addition of 4,4′-dimethoxybenzophenone 9 results in an increased yield and also alters the stereochemical outcome leading to preferential isolation of the trans dihydrobenzofurans 6a–8a (up to 50% yield), while the cis and trans diastereomers of 6–8 are recovered in essentially equimolar amounts in the absence of a photosensitiser (up to 26% yield).