Copper-catalyzed regio- and enantioselective addition of silicon Grignard reagents to alkenes activated by azaaryl groups

A new application of silicon Grignard reagents in C(sp${}^3$)-Si bond formation is reported. With the aid of BF${}_3$⋅OEt${}_2$, these silicon nucleophiles add across alkenes activated by various azaaryl groups under copper catalysis. An enantioselective version employing benzoxazole-activated alkenes as substrates and a CuI-josiphos complex as catalyst has been developed, forming the C(sp${}^3$)-Si bond with good to high enantiomeric ratios (up to 97:3). The method expands the toolbox for "conjugate addition" type C(sp${}^3$)-Si bond formation. (© 2019 Wiley-VCH Verlag GmbH & Co. KGaA, Weinheim)