A Convergent, Stereoselective Route to Trisubstituted Alkenyl Boronates.

A modular, stereoselective route to trisubstituted (Z)-alkenyl (MIDA)boronates is described, consisting of the radical addition-fragmentation of dithiocarbonates to 2-(MIDA)boronyl-3-(2'-fluoro-pyridyl-6'-oxy)-alkenes. The bulky (MIDA)boronate ensures a highly stereoselective fragmentation that is enhanced by the poor stabilization of the radical adjacent to the tetravalent boron atom. The vinyl boronate precursors are prepared from propargyl alcohols by copper-catalyzed regioselective protoboration of their fluoropyridoxy derivatives, with the fluoropyridine acting as an internal directing group.