Organocatalytic enantioselective synthesis of acyclic pyrimidine nucleosides by aza-Michael reaction.

An efficient diarylprolinol triphenylsilyl ether-catalyzed enantioselective aza-Michael reaction of pyrimidines as N-centered nucleophiles to α,ß-unsaturated aldehydes, followed by reduction, provided chiral acyclic pyrimidine nucleosides in good yields (51-78% yields for two steps) and excellent enantioselectivities (91-98% ee). In addition, the chiral acyclic pyrimidine nucleoside having the tert-butyldiphenylsilyl-protected hydroxyl substituent was successfully applied to the synthesis of the corresponding chiral cyclic pyrimidine nucleoside analogue bearing the tetrahydrofuranyl ring.