Electrophilic glycosidation employing 3,5-O-(di-tert-butylsilylene)-erythro-furanoid glycal leads to exclusive formation of the β-anomer: synthesis of 2′-deoxynucleosides and its 1′-branched analogues

Abstract Stereoselectivity in N -iodosuccimide (NIS)-mediated electrophilic glycosidation was examined by employing 2,4-bis- O -(trimethylsilyl)thymine and three different silyl-protected erythro -furanoid glycals 12 , 16 , and 18 . As a result, it was found that 3,5- O -(di- t -butylsilylene)-protected 18 gave only the β-anomer ( 21 ). The remarkable stereoselectivity observed by employing 18 is discussed on the basis of its X-ray crystallographic analysis. 1-Substituted glycals gave the corresponding β-anomer, again exclusively, to provide access to 1′-branched 2′-deoxynucleosides.