Access to chiral α-bromo and α-H-substituted tertiary allylic alcohols via copper(I) catalyzed 1,2-addition of Grignard reagents to enones

The catalytic asymmetric synthesis of tertiary alcohols by the addition of organometallic reagents to ketones is of central importance in organic chemistry. The resulting quaternary stereocentres are difficult to prepare selectively by other means despite their widespread occurrence in natural products and pharmaceuticals. Here we report on a new methodology which allows access to both alpha-bromo-substituted and alpha-H-substituted allylic tertiary alcohols with excellent yields, and enantioselectivities of up to 98% using the copper(I)-catalysed 1,2-addition of Grignard reagents to enones. As an example, the methodology is applied in the synthesis of a chiral dihydrofuran.