An Efficient Approach for the Synthesis of 1′-O-α-Methyl Pyrrolo[2,3-d]pyrimidine Isonucleosides

A series of novel 1'-O-alpha-methyl isonucleosides were efficiently and stereoselectively synthesized with 1,2,3,5-tetra-O-acetyl-D-ribofuranose as the starting material. The key steps include regioselective and stereoselective deprotection of the 2,4-dichlorobenzyl group at C2, triflation, and substitution with appropriate nucleobases using cesium carbonate as the base. Removal of the residual 2,4-dichlorobenzyl groups and subsequent transformation afforded the title compounds in 30-37% overall yield. The products represent a new type of isonucleosides with 1'-O-substitution.