Construction of a CF 3 -Containing Benzofurofuranone Skeleton from Coumarins via Reductive Coupling and Acid-Mediated Ring Contraction.

Magnesium-promoted reductive introduction of a trifluoroacetyl group to coumarin in the presence of ethyl trifluoroacetate and the subsequent treatment with trifluoro- acetic acid led to simple access to a trifluoromethylated benzofurofuranone at 8a-position with a high regio- and stereoselectivity. Trifluoromethylated or difluoromethylated benzofurofuranone derivatives were also prepared from coumarins including naturally occurring ones only in two successive steps, which might have potential bioactivity in medicinal chemistry.