Facile Synthesis of 2′‐Deoxyribofuranosides of Allopurinol and 4‐Amino‐1 H ‐pyrazolo[3,4‐ d ]pyrimidine via Phase‐Transfer Glycosylation

Phase‐transfer glycosylation of 4‐methoxy‐1 H ‐pyrazolo[3,4‐ d ]pyrimidine with the 2‐deoxyribofuranosyl chloride 9 formed the N(1)‐β‐nucleoside 10a as main product (39%). As by‐products the α‐ D ‐anomer 11a (7%) and the N(2)‐isomer 12a (18%) were isolated. Assignment of these isomers was made on the basis of their 1 H‐ and 13 C‐NMR spectra. Removal of the sugar‐protecting groups yielded the 4‐methoxy‐nucleosides 10b, 11b , and 12b , respectively. Nucleophilic displacement of the 4‐MeO‐group gave the 2‐deoxyribofuranosides 1–4 of allopurinol and 4‐amino‐1 H ‐pyrazolo[3,4‐ d ]pyrimidine.