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Communication | Regular issue | Vol 20, No. 6, 1983, pp.995-1000
Published online, 1st January, 1970
DOI: 10.3987/R-1983-06-0995
Pyrazole N- and C-β-D-Ribofuranosyl Nucleosides. Synthesis of Some β-D-Ribofuranosyl-4,7-methanoindazoles and Pyrazolo[1,5-a]azepines

Shin-ichi Nagai, Taisei Ueda, Noriichi Oda, and Jinsaku Sakakibara

*Faculty of Pharmaceutical Sciences, Nagoya City University, Tanabe-dori, Mizuho-ku, Nagoya 467-8603, Japan

Abstract

Condensation of O-isopropylidene-D-ribosylhydrazine (1) with (1R,4S)-3-hydroxymethylenebornan-2-ones (2a-b) led to selective N-1 ribosylation of pyrazole ring to provide (4S,7R)-1-(2,3-O-isopropylidene-β-D-ribofuranosyl)-4,5,6,7-tetrahydro-4,7-methano-1H-indazoles (3a-b), and deprotected 4,7-methano-1H-indazole (4) after treatment with methanolic HCl. Structure determination including anomeric configuration assignment was discussed based on 1H-NMR spectroscopy. 1,3-Dipolar cycloaddition of diazoketone (5) with β-D-ribofuranosylpropiolate (8) followed by [1,5]sigmatropic rearrangement was used as a key reaction step in a novel synthesis of pyrazole C-ribofuranoside, (4S,7R)-3-(2,3-O-isopropylidene-5-O-trityl-β-D-ribofuranosyl)-8-oxo-4,7-methano-8H-pyrazolo[1,5-a]azepine (11). The protective groups of 11 were easily removed by methanolic HCl to give 3-(β-D-ribofuranosyl)-8H-pyrazolo[1,5-a]azepine (12).