Diastereoselective addition of allyl reagents to variously N-monoprotectedand N,N-diprotected L-alaninals

Diastereoselective C-3-clongation processes of N-Boc-, N-Z-, N-Bn-N-Boc-, a nd N-Bn-N-Z-L-alaninals (Boc = BuOCO, Z PhCH2OCO, Bn = PhCH2) using various allyl reagents, such as allyl bromide in the presence of Zn/aqueous NH4Cl solution. of SnCl2 . 2 H2O/NaI or of Mg/CuCl2 . 2 H2O, as well as allyltric hlorosilane. are described. A substantially different influence of the N-pr otecting groups replacing either one or two amino protons was observed, all owing the selective synthesis of either the syn- or anti-diastereoisomer as a major product.