Visible-light-mediated cascade cyanoalkylsulfonylation/cyclization of alkynoates leading to coumarins via SO2 insertion.

ABSTRACT

A visible-light-mediated tandem cyanoalkylsulfonylation/cyclization of alkynoates with cycloketone oxime compounds for the preparation of 3-cyanoalkylsulfonylcoumarins via SO2 insertion is reported. The difunctionalization of carbon-carbon triple bonds includes a radical mechanism and involves the formation of an iminyl radical, ring-opening of the cycloketone, insertion of SO2, addition of the sulfonyl radical to carbon-carbon triple bonds, ipso-cyclization and ester migration.