The Clemmensen Reduction of α, β-Unsaturated Ketones

✍ Scribed by Charles W. Jefford; André F. Boschung

• Publisher: John Wiley and Sons
• Year: 1976
• Tongue: German
• Weight: 525 KB
• Volume: 59
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19760590328

✦ Synopsis

Abstract

Eleven structurally different α, β‐unsaturated ketones were subjected to the Clemmensen reduction under anhydrous conditions using amalgamated zinc, hydrogen chloride in a solution of ethyl ether, and acetic anhydride. In all cases but one the formation of cyclopropyl acetates was observed. 4‐Methyl‐3‐penten‐2‐one, methyl vinyl ketone, 2‐isopropylidene‐1‐cyclopentanone, and 2‐cyclohepten‐1‐one led to substituted cyclopropyl acetates. Stereospecific reactions were found with 2‐ethylidene‐1‐cyclopentanone, 2‐benzylidene‐1‐cyclohexanone, and methyl 1‐cyclohexenyl ketone, whereas 3‐penten‐2‐one, 3‐methyl‐3‐buten‐2‐one, and 2‐methyl‐2‐cyclohexen‐1‐one afforded mixtures of the isomeric cyclopropyl acetates.

These results are interpreted in terms of the intital formation of an allylic anion which undergoes electrocyclic closure. A stereospecific course is followed when geometric constraints permitted. Exceptions are discussed.