Detection and elimination of product inhibition from the asymmetric catalytic hydrogenation of enamines

[GRAPHICS] The catalytic asymmetric hydrogenation of enamine amides and esters with catalyst Rh-la, prepared from ferrocenyl based ligand 1a or 1b and [(COD)RhCl](2), has been shown through kinetic studies to suffer from product inhibition. Enamine ester substrates have also been shown to be incompatible with the amine products of the reaction in methanol. In situ protection of the amine products with di-tert-butyl dicarbonate eliminates functional group incompatibility of ester substrates and eliminates product inhibition in the reaction.