Copper-Catalyzed Ring-Opening Defluoroborylation of gem -Difluorinated Cyclobutenes: A General Route to Bifunctional 1,3-Dienes and Their Applications.

The exploration of the reactivity of gem -difluorinated small-size rings has continuously drawn attention in recent years but is limited to three-membered carbocycles. Herein we report a copper-catalyzed reaction of gem -fluorinated cyclobutenes with bis(pinacolato)diboron (B 2 pin 2 ). A sequence of defluoroborylation and a ring-opening process produces B,F-bifunctional 1,3-dienes in a stereoselective manner. The transformation together with the efficient downstream coupling of the boronate and the fluoride moieties collectively constitutes a modular route to highly functionalized and stereocontrolled 1,3-dienes.