Abstract
3-Phenyl-4-(β-and-α-D-ribofuranosyl) pyrazoles (1a) and (2a) have been synthesized from 2, 3, 5-tri-O-benzoyl-D-ribofuranosyl bromide (3) by the substitution of 3 with bisphenylethynyl) mercury (4a) into 1-phenyl-2-(2, 3, 5-tri-O-benzoyl-β- and -α-D-ribofuranosyl) ethynes (5a) and (6a) and subsequent addition reaction with diazomethane. Ethynylation of 3 with 4a have furnished a mixture of 5a and 6a, however, with phenylethynylcopper (4b) the ketal (7a) was formed together with 5a. The configuration of the anomeric carbon of the major product (5a) was proved by its permanganate oxidation into the known tri-O-benzoylallonic acid (5d). The nuclear magnetic resonance spectra of the 2, 3-O-isopropylidene ribofuranosyl derivatives (9a-d) and (10a-d) have shown that the coupling constant of the proton at the anomeric carbon is approximately 4 Hz in the 1-α-substituted anomer, and, on the other hand, almost negligible in the 1-β-substituted anomer. Both acetylenic compounds (5a) and (6a) were converted into ribosyl pyrazole (5f) and (6c) by 1, 3-dipolar addition reaction with diazomethane, which were finally debenzoylated with ammonia into the triols (1a) and (2a), respectively.
