The synthesis of d-ribofuranosyl derivatives of methyl propiolate and a study of the activating influence of the ester group in cylcoaddition reactions

2,3,5-Tri-O-benzyl-D-ribofuranosyl bromide (17) has been converted into methyl 3-(2,3,5-tri-O-benzyl-β-d-ribofuranosyl)propiolate (8) and its α anomer 10 in 21 and 42% yields, respectively, by reaction with the silver salt of methyl propiolate. Attemps to prepare 8 from (β-d-ribofuranosyl)ethyne (1) by standard methods were unsuccesful. The reactions of the esters 8 and 10 and the ethyne 1 with several 1,3-dipoles have been examined. With diazomethene, 8 and 10 gave the pyrazole esters 20 and 28, respectively, whereas 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.