The synthesis of a variety of chemically modified oligonucleotides requires the development of a practical synthetic method for its building block, i.e., nucleoside analogs. The one-pot Pummerer-like reaction using hypervalent iodine in combination with 6-chloropurine and an ‘armed’ 4-selenosugar bearing an electron-donating group at the 2-position gave the desired 4′-seleno-6-chloropurine derivative