Either the α- (3) or γ-amino acid derivatives (4) can be prepared with very high regioselectivity by treating diethyl azodicarboxylate (DEAD) with (i) lithium dienolates themselves (2) in certain cases, (ii) Sn-masked dienolates (5), or (iii) Ge-masked dienolates (6).
Stabilization and activation of dienolates with germanium and tin. Stereo- and regioselective aldol reactions, regioselective coupling reactions, and regioselective synthesis of amino acid derivatives