Addition of hydrogen chloride to an allylidenecyclopropane; survival of the cyclopropane ring

✍ Scribed by Marvin L. Poutsma; Pedro A. Ibarbia

• Publisher: Elsevier Science
• Year: 1970
• Tongue: French
• Weight: 173 KB
• Volume: 11
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(00)89322-3

✦ Synopsis

Recently we described (1) the acid-catalyzed rearrangement of allene 1 to form a mixture of ring-opened isomers 2 (major) and 2 (minor); these conversions were rationalized as proceeding by the carbonium ion pathways shown. In particular, acid-catalyzed rearrangement of 2-methyl-3-(tetrsmethylcyclopropylidene)-propene (k), available frcan base-catalyzed isomerization of allene A, gave triene 2 cleanly. Thus protonation of either allene t or diene : offered routes to cation 2 which could reasonably give triene 2 after electrocyclic ring opening to form cation $ followed by proton loss. However, since solvolysis of most cyclopropyl derivatives gives allylic cations in a concerted fashion without the intervention of discrete cyclopropyl cations (2), it was of interest to determine whether cation 2, one resonance structure of which is a vinyl-substituted cyclopropyl cation, represents an energy minimum in the conversion of diene 5 to triene 2. We now report evidence for trapping of a