Synthèse de spiro-pyrazolines par cycloaddition du diazométhane sur des sucres insaturés ramifiés. Influence de l'isomérie géométrique sur l'orientation de la réaction Communication préliminaire

✍ Scribed by Jean M. J. Tronchet; Bernard Gentile; Jeannine Tronchet

• Publisher: John Wiley and Sons
• Year: 1975
• Tongue: German
• Weight: 366 KB
• Volume: 58
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19750580637

✦ Synopsis

Abstract

The orientation of the cycloaddition of diazomethane on unsaturated branchedchain sugars has been studied. For 3‐C‐cyanomethylidene‐3‐deoxy‐1,2‐O‐isopropylidene‐α‐D‐glycero‐tetrofuranose the orientation was ‘normal’ and did not depend on the configuration at the double bond. The same situation prevailed with derivatives of 3‐deoxy‐1,2:5,6‐di‐O‐isopropylidene‐3‐C‐methylidene‐α‐D‐xylo‐hexofuranose. For the 3‐C‐acylmethylidene‐ and the 3‐C‐cyanomethylidene‐3‐deoxy‐1,2:5,6‐di‐O‐isopropylidene‐α‐D‐ribo‐hexofuranoses, the trans‐(H–C(3′)–C(2))‐isomer gave the ‘normal’ cycloadduct whereas the cis‐isomer gave predominantly the αabnormal spiro‐pyrazoline. This observation represents the first instance where the regioselectivity of a cycloaddition reaction is affected by the geometrical isomerism of the dipolarophile. The most probable explanation of the phenomenon is the conformational perturbation about the C(4)‐‐C(5) bond of the unsaturated sugars induced by a change in the configuration at C(3). The consequence of that ‘conformational transmission’ of a difference in configuration at C(3) is that the steric crowding on the cis‐ than in the trans‐isomer. Several novel examples of a new series of C‐glycosylidenic derivatives, the spiro‐pyrazolines, are described.