Based on a novel concept, a Reducing-Environment-Dependent Uncatalyzed Chemical Transforming RNA, “REDUCT RNA”, we established a post-synthetic approach for the synthesis of 2′-O-methyldithiomethyl-modified oligonucleotides from 2′-O-(2,4,6-trimethoxybenzylthiomethyl)-oligonucleotides by treatment with dimethyl(methylthio)sulfonium tetrafluoroborate. 2′-O-methyldithiomethyl oligonucleotides were easily converted into 2′-hydroxy oligonucleotides under reducing conditions, such as those found in the intracellular environment.