Stereoselective Nucleophilic Addition Reactions of Reactive Pseudopeptides

D,L-Pseudopeptides of type 1 undergo 1,4-additions with tBu2CuLi/Me3SiCl with high stereoselectivity, whereas reactions of the corresponding L,L diastereomers are substantially less diastereoselective. The L,L,L and D,L,L analogues also react with different stereoselectivities. Strict chelation control plays a role in the Grignard-like reaction of L,L peptide aldehydes like 2 with (CH3)2CuLi.