β‐Ribo‐ and α‐arabinonucleosides containing the 1,2‐benzisoxazole and 1,2‐benzisothiazole rings

The reaction of the silylated base of 1,2‐benzisoxazol‐3(2 H )‐one ( 1 ) and its 7‐methyl derivative 5 and 5‐methyl‐1,2‐benzisothiazol‐3(2 H )‐one ( 9 ), respectively, with 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐β‐D‐ribofuranose followed by basic deprotection gave the corresponding β‐D‐ribonucleosides, and the silylated base of 1 , when treated with 1‐ O ‐acetyl‐2,3,5‐tri‐ O ‐benzoyl‐α‐D‐arabinofuranose in the presence of stannic chloride, afforded the corresponding α‐arabinonucleoside. Structural proofs of these nucleosides are provided from elemental analyses and 1 H and 13 C nmr spectra.