<i>syn</i> -Selective α-Boration-Arylation of Alkynes: Concise Access to Configurationally Defined Tetrasubstituted Alkenes

Hydro- and heteroboration of alkynes typically delivers a boron substituent at the β-position. Herein, <i>syn</i>-selective α-borylation-arylation is accomplished through a one-pot Ni-catalyzed carbomagnesiation followed by borylation. The regio- and stereoselectivity is established in the carbometalation step, while utilization of B(pin)H is essential for high efficiency of borylation of the sterically hindered vinylmagnesium intermediate. The resulting trisubstituted vinyl boronates are versatile building blocks, in particular, for the synthesis of configurationally defined tetrasubstituted olefins through cross-coupling. A two-step synthesis of Tamoxifen is presented.