Stereoselective synthesis of trisubstituted vinylboronates from ketone enolates triggered by 1,3-metalate rearrangement of lithium enolates

An unprecedented stereoselective synthesis of trisubstituted vinylboronates is reported to proceed by direct borylation of lithium ketone enolates under transition-metal-free conditions. The stereospecific C-O borylation of lithium enolates was triggered by a carbonyl-induced 1,3-metalate rearrangement via a C-bound boron enolate. DFT calculations and control experiments revealed that the stereoselectivity is controlled by sterics. A variety of stereospecific trisubstituted vinylboronates, together with several tetrasubstituted vinylboronates, were conveniently synthesized with the newly developed methodology. Based on the transformation of stereospecific vinylboronate, a single isomer of Dienestrol was efficiently obtained. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)