General preparative synthesis of 2′‐ O ‐methylpyrimidine ribonucleosides

A convergent and general approach to synthesizing 2′‐ O ‐Methylpyrimidine ribonucleosides 4a‐e, 6,7 on a multigram scale is described which begins with an improved procedure for making larger quantities of 2‐ O ‐methyl‐1,3,5‐tri‐ O ‐benzoyl‐α‐D‐ribose. The sugar was reacted with the desired silylated pyrimidines at room temperature under Vorbrüggen conditions. The crude products contained less than 10% of the α anomers and the desired β anomers were isolated by crystallization. The blocked nucleosides were then deprotected and isolated by standard methods.