4-Aminothiourea Prolinol tert-Butyldiphenylsilyl Ether: A Chiral Secondary Amine-Thiourea as Organocatalyst for Enantioselective anti-Mannich Reactions

anti-Selective Mannich reactions of N-p-methoxyphenyl (PMP)-protected alpha-iminoglyoxylate with unmodified aldehydes or ketones were effectively catalyzed by 4-aminothiourea prolinol tert-butyldiphenylsilyl ether. The reactions led to chiral beta-amino carbonyl compounds in high yields (up to 94%), excellent diastereo- and enantioselectivities (up to 98% de and > 99% ee). The study demonstrated for the first time that direct Mannich-type reactions of unmodified aldehydes or ketones to alpha-iminoglyoxylate can be promoted by secondary amine-thiourea chiral organocatalyst.