Chemo- and stereoselective Grignard addition reactions are possible if ligand tuning is applied, as in the magnesiation of akyllithium reagents with magnesium tosylates or carboxylates. Protective groups tuning is another important instrument. Thus, N,N-dibenzyl- amino aldehydes react with a variety of organometallics under non-chelation conuol. The nature of the protective group is also important in reactions of a-amino aldimines and electron-poor y-aminoolefms (including peptide derivatives).