Diastereoselective Synthesis of ψ[(E)-CHCMe]- and ψ[(Z)-CHCMe]-Type Dipeptide Isosteres by Organocopper-Mediated anti-S_N2‘ Reaction

Acyclic ψ[(E)-CHCMe]- and ψ[(Z)-CHCMe]-type dipeptide isosteres were efficiently synthesized. In a key reaction, α-alkylation of γ-mesyloxy-β-methyl-α,β-unsaturated esters with organocyanocuprates in diethyl ether or tetrahydrofuran preferentially afforded the ψ[(E)-CHCMe]- or ψ[(Z)-CHCMe]-isomer, respectively, via anti-S_N2‘ mechanism.