Difluorocarbene-Mediated Cascade Cyclization: The Multifunctional Role of Ruppert-Prakash Reagent.

A difluorocarbene-mediated cascade cyclization reaction for rapid access to gem-difluorinated 3-coumaranone derivatives was developed. The difluorocarbene acts as a bipolar CF2 building block, which enables a homologation cyclization process via sequentially reacting with the phenolate and the ester group on the same substrate. The potential application of this synthetic approach is demonstrated by a late-stage modification of diethylstilbestrol. Mechanistic studies revealed the multiple crucial roles played by the Ruppert-Prakash reagent.