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Nucleoside synthesis: A systematic study of the influence of the nature and stereochemistry of d-aldopentofuranoses, and the effect of the substituent at C-2, in the acid-catalyzed fusion-reaction with indazole

✍ Scribed by Bernard L. Kam; Jean-Louis Barascut; Jean-Louis Imbach

Publisher
Elsevier Science
Year
1980
Tongue
English
Weight
368 KB
Volume
78
Category
Article
ISSN
0008-6215

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✦ Synopsis

A systematic study of the acid-catalyzed fusion-reaction is reported. The influence of the nature and stereochemistry of the D-aldopentofuranose and the effect of the substituent at C-2 have been investigated by using indazole as a model heterocycle. The results obtained show that the nature and stereochemistry of the starting, per-O-acctylated D-aldopentofuranose have no significant effect upon the product distribution of the acid-catalyzed fusion-reaction. The use of a sugar lacking a participating group at C-2 showed, however, that the absence of participation increases the ratio of cis-1 ',2'-nucleosides, and the mechanism involved is discussed. [n all cases, the results indicated that the distribution of the products is determined by their relative, thermodynamic stabilities.

I NTRODUCTI[)N

The fusion reaction is one of the most recent methods introduced for the synthesis of nucleosides'. This technique for forrnation of a C-N linkage is simple and rapid, and has been extensively used 2-9. Because few systematic studies of this reaction have been reported '°'l~, there are many discrepancies in the literature concerning the obtaining of different anomers and isomers 2-9. In order to resolve these problems in the aldopcntofuranose series, ~e have investigated the condensation of indazole (1) with per-O-acetylated D-aldopentofuranoses.

Previously, we reported the influence of vacuum, catalyst, temperature, and reaction time upon the distribution of the products generated by the acid-catalyzed fusion-reaction 11, and showed that it is possible to orient the reaction towards the favored formation of a desired isomer. Furthermore, the results permitted us to

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