We have investigated on the reaction of an organotin amide compound of general formula (IV): ##STR4## wherein one of R4 and R5 is an alkyl or aryl group and the other is a hydrogen atom or an alkyl or aryl group with a deoxynucleoside or deoxynucleotide of general formula (V): ##STR5## wherein R2, R3, B and n have the same meanings as defined above and now found that the reaction proceeds accordin