Unexpected effects of Lewis acids in the synthesis of optically pure 2′-deoxy-3′-oxacytidine nucleoside analogues

Abstract TiCl 4 and SnCl 4 promote the formation of dioxolane nucleosides with racemization in the coupling of enantiomerically pure 2′-deoxy-3′oxaribosides with silylated N -acetylcytosine. The use of TMSOTf, TMSI or TiCl 2 (Oi-Pr) 2 furnishes enantiomerically pure cytosine dioxolane nucleosides in low diastereoselectivity.