Synthesis of optically active polycyclic N-heterocycles derived from l-prolinamine1

Abstract The N -Boc-protected ( S )-prolinamine reacts readily with formaldehyde and diverse α-hydroxyimino ketones to give imidazole N -oxides with an enantiomerically pure N -protected (pyrrolidin-2-yl)methyl substituent. Subsequent deprotection yields the corresponding NH derivatives. Upon treatment of these products with Ac 2 O at room temperature, a cascade of reactions leads to optically active tricyclic products. In all these processes, the stereogenic center is preserved. In one case, the bis-heterocyclic imidazole N -oxide was transformed into the corresponding optically active imidazole-2-thione via a sulfur-transfer reaction with 2,2,4,4-tetramethylcyclobutane-1,3-dithione.