C‐Glycosides VI. Modalités de l'élaboration de cycles pyrazoliques à partir d'une hydrazone d'<i>aldéhydo</i>‐sucre

Abstract

Abstract The reaction of an aldehydo ‐sugar hydrazonoyl bromide with ethynylmagnesium bromide led mainly to an α‐ethynyl‐hydrazone whose cyclisation to a pyrazole is catalysed by bases. Thus the nucleophilic substitution – nucleophilic cyclisation mechanism of the Grünanger pyrazole synthesis is confirmed. 3‐Glycosyl‐pyrazoles can also be prepared from aldehydo ‐sugar hydrazonoyl bromides by 1,3‐dipolar cyclo‐addition. All these reactions take place without change in the configuration of the initial aldehydo ‐sugar.