New protecting groups having a 2-aminomethylbezoyl skeleton, in which the reactive amino functions were blocked further by a tritylthio-type protecting group, were developed for the protection of the 5'-hydroxyl function of nucleosides during the oligonucleotide synthesis. These benzoate-type protecting groups were designed to be removed via an intramolecular cyclization following the removal of the tritylthio-type protecting group under mild oxidative conditions using diluted aqueous iodine solution. The new protecting groups would enable us to synthesize oligonucleotides without using any acid treatment. Furthermore, they can reduce the reaction steps required for a chain elongation cycle from four to three because the deprotection of the 5'-hydroxyl protecting group and the oxidation of the phosphite intermediate can be performed simultaneously by a single aqueous iodine treatment.