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The Ring Closure of Cyclopenta-1, 3-dien-5-yl-carbene to Benzvalene. A mechanistic study of an unusual carbene reaction

✍ Scribed by Ulrich Burger; Gérard Gandillon; Jiri Mareda

Book ID
102859103
Publisher
John Wiley and Sons
Year
1981
Tongue
German
Weight
545 KB
Volume
64
Category
Article
ISSN
0018-019X

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✦ Synopsis

Abstract

The base‐induced α‐elimination of hydrogen chloride from 5‐chloromethyl‐5‐methylcyclopenta‐1, 3‐diene (19) produces 1‐methyltricyclo [3.1.0.0^2,6^]hexene‐3 (1‐methylbenzvalene) (21) together with toluene and spiro [4.2]heptadiene (23). A common intermediate, 5‐methylcyclopenta‐1, 3‐dien‐5‐yl‐carbene (20), accounts for these results by intramolecular 1, 4‐carbene addition, 1, 2‐carbon shift and CH‐insertion, respectively. Independent synthesis of 2‐methylbenzvalene (24) allows us to show that the classic intramolecular cyclopropanation is completely suppressed by the linear cheletropic ring closure. MINDO/3 predicts the key carbene to have a bisected conformation in its singlet ground state. This ideally fulfills the stereoelectronic conditions for a carbene reaction of least motion. The influence of the methyl substituent upon that process is discussed.

📜 SIMILAR VOLUMES

The ring closure of 5-methylcyclopenta-1
The ring closure of 5-methylcyclopenta-1,3-dien-5-ylcarbene to 1-methylbenzvalene. An intramolecular 1,4 cheletropic carbene addition
✍ Ulrich Burger; Gérard Gandillon 📂 Article 📅 1979 🏛 Elsevier Science 🌐 French ⚖ 180 KB

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## Abstract The 4‐substituted 1‐phenyl‐1‐butene‐3‐ynes 1a–c and the 2‐ethynylstyrenes 7a–c were subjected to high‐temperature pyrolysis. The cycloisomerization products isolated suggest that these are formed by three competing processes: by (i) an electrocyclic or a molecule‐induced, (ii) an alkeny