γ-Monosubstituted and trans-α,β-disubstituted γ-lactams were diastereoselectively synthesized from common intermediates (S)-N,N-dibenzylated aldehydes derived from natural l-(α)-amino acids, employing a divergent approach. The key features of the routes include diastereoselective Henry and Michael reactions that produced chiral γ-nitroester derivatives, which were subsequently submitted to a tandem reduction-lactamization sequence providing the title compounds. The versatility of routes can allow the preparation of several other mono-, di-, or tri-substituted γ-lactams.