The synthesis of D-ribofuranosyl derivatives of methyl propiolate and a study of the activating influence of the ester group in cycloaddition reactions.

2,3,5-Tri-O-benzyl-D-ribofuranosyl bromide (17) has been converted into methyl 3-(2,3,5-tri-O-benzyl-beta-D-ribofuranosyl) propiolate (8) and its alpha anomer 10 in 21 and 42% yields, respectively, by reaction with the silver salt of methyl propiolate. Attempts to prepare 8 from (beta-D-ribofuranosyl)ethyne (1) by standard methods were unsuccessful. The reactions of the esters 8 and 10 and the ethyne 1 with several 1,3-dipoles have been examined. With diazomethane, 8 and 10 gave the pyrazole esters 20 and 28, respectively, whereast the ethyne 1 reacted more slowly to give a mixture of 23 (37%) and 26 (31%). The ester 10 was converted into the triazoles 32 (51%) and 36 (34%) by reaction with benzyl azide. Treatment of the ester 10 with phenylhydrazine gave the pyrazolone 38 in 71% yield. A number of the products of dipolar addition have been converted into new D-ribofuranosyl-pyrazoles and -triazoles by hydrogenolysis.