Diastereoselective Copper-Mediated Cross-Couplings between Stereodefined Secondary Alkylcoppers with Bromoalkynes.

A copper(I)-mediated cross-coupling of stereodefined secondary alkyllithiums with bromoalkynes provided stereodefined alkynes with high diastereoselectivity (dr up to 98:2). This cross-coupling was extended to various secondary alkyllithiums bearing a remote oxygen functionality, and the alkyne synthesis was also performed with optically enriched alkyl iodides (up to 99% ee) providing, after cross-coupling, alkynes bearing two stereocenters (dr = 93:7; up to 99% ee).