Primary Amine-Thioureas with Improved Catalytic Properties for Difficult Michael Reactions: Efficient Organocatalytic Syntheses of (S)-Baclofen, (R)-Baclofen and (S)-Phenibut

Among the class of primary amine-thioureas based on tert-butyl esters of a-amino acids, the most efficient organocatalyst for difficult Michael reactions was identified. The derivative based on (S)-di-tert-butyl aspartate and (1R,2R)-diphenylethylenediamine provided the products of the reaction between aryl methyl ketones and nitroolefins in excellent yields and enantioselectivities. In addition, this new catalyst can be used at low catalyst loading (5 mol%). The utility of this methodology was highlighted by the efficient synthesis of (S)-baclofen, (R)-baclofen and (S)-phenibut.