Visible-light-induced cascade radical cyclization of aryl alkynoates with fluoroalkyl carboxylic anhydrides to construct fluoroalkylated coumarins

We herein described an efficient and practical protocol for radical cyclization of aryl alkynoates to access 3-fluoroalkyl-substituted coumarins using readily available, easy-to-handle and low-cost fluoroalkyl carboxylic anhydride as fluoroalkyl source. This method is featured by its generally applicable to several kinds of fluoroalkyl carboxylic anhydrides including difluoromethy1, trifluoromethyl, pentafluoroethyl, heptafluoropropyl and chlorodifluoromethyl, as well as a good functional group tolerance with respect to a wide variety of aryl alkynoates. This reaction was triggered by addition of fluoroalkyl radical to the triple bond of alkynoates, followed by a cascade 5- exo cyclization/oxidization/1,2-ester migration/rearomatization process. We developed the visible-light-induced cascade radical cyclization of aryl alkynoates with readily available fluoroalkyl carboxylic anhydride as fluoroalkyl radical source, providing a practical and general approach to various 3-fluoroalkyl coumarins, including difluoromethyl, trifluoromethyl, pentafluoroethyl, heptafluoropropyl and chlorodifluoromethyl, in good to excellent yields. The reaction involved a cascade 5- exo cyclization/oxidization/1,2-ester migration/rearomatization process.