Reaction of deoxynucleoside 3'-O-(methylthiomethyl) acetals 1 with N-iodosuccinimide (NIS) and dibutyl phosphate furnished the corresponding 3'-O-(dibutoxyphosphoryloxy)methyl acetals 6. Condensation of the latter with appropriately protected deoxynucleoside acceptors 3, in the presence of trimethylsilyl trifluoromethanesulfonate (TMSOTf), afforded in most cases the (3'→5') methylene acetal linked d(B 1Λ B 2 ) dimers 4. In addition, TMSOTf-promoted coupling of donor 6 (B 1 =C Bz ) with 3'-O-(methylthiomethyl)thymidine (8) yielded dimer 9. Reaction of 9 with NIS and dibutyl phosphate gave dimer 10, which was applied successfully in the TMSOTf-assisted fusion with acceptor 3 (B 2 =C Bz and A Bz ), to afford the corresponding trimers d(C Λ T Λ C) 11 and d(C Λ T Λ A) 12