Expedient asymmetric synthesis of all four isomers of N,N '-protected 2,3-diaminobutanoic acid

2,3-Diaminobutanoic acid (DAB) is found in several peptide antibiotics, tox ins, and biologically active molecules. This paper describes the practical and highly enantioselective synthesis of all four N,N'-protected DAB stereo isomers using an asymmetric Rh(I)-phosphine-catalyzed hydrogenation of isom eric enamides as the key step. Thermal and photochemical isomerization of t he enamide hydrogenation substrates coupled with catalyst-geometric isomer pairing allows targeted synthesis of single DAB isomers in maximum yield.