Enantioselective Biginelli Reaction of Aliphatic Aldehydes Catalyzed by a Chiral Phosphoric Acid: A Key Step in the Synthesis of the Bicyclic Guanidine Core of Crambescin A and Batzelladine A
applied in the formal synthesis of the bicyclicguanidine core of crambescin A and batzelladine A. An efficient chiral phosphoric acid catalyzed Biginelli reaction for the synthesis of optically pure 4-alkyl-3,4-dihydropyrimidin-2-(1H)-ones has been developed, with a wide range of the desired products being obtained in moderate to high yields with good to excellent enantioselectivities (up to >99% ee