Asymmetric organocatalytic synthesis of tertiary azomethyl alcohols: key intermediates towards azoxy compounds and α-hydroxy-β-amino esters

A series of peracylated glycosamine-derived thioureas have been synthesized and their behavior as bifunctional organocatalysts has been tested in the enantioselective nucleophilic addition of formaldehyde tert-butyl hydrazone to aliphatic alpha-keto esters for the synthesis of tertiary azomethyl alcohols. Using the 1,3,4,6-tetra-O-acetyl-2-amino-2-deoxy-beta-D-glucosamine derived 3,5-bis-(trifluoromethyl) phenyl thiourea the reaction could be accomplished with high yields (75-98%) and moderate enantioselectivities (50-64% ee). Subsequent high-yielding and racemization-free tranformations of both aromatic-and aliphatic-substituted diazene products in a one pot fashion provide a direct entry to valuable azoxy compounds and alpha-hydroxy-beta-amino esters.