Investigation of the Cyclopentenone Formation via the α-Alkynone Cyclisation: Synthesis of the Acorone Intermediate 8-Methylspiro[4.5]deca-3,7-dien-2-one

✍ Scribed by John Ackroyd; Martin Karpf; André S. Dreiding

• Book ID: 102856799
• Publisher: John Wiley and Sons
• Year: 1985
• Tongue: German
• Weight: 501 KB
• Volume: 68
• Category: Article
• ISSN: 0018-019X
• DOI: 10.1002/hlca.19850680208

✦ Synopsis

Abstract

As a further application of the cyclopentenone formation A→C via the thermal α‐alkynone cyclisation B→C and in order to test the fate of an isolated C,C‐double bond within a molecule under these conditions, we investigated the synthesis of the acorone intermediate 3starting from the known carboxylic acid 1. The α‐alkynone 2 was obtained from 1 via the acyl chloride 6 and a Pd(II)‐catalysed route (22%). The thermolysis of 2 at 550° provided the target molecule 3 (48%) together with the product 9 (20%) of a competing intramolecular ene reaction and its dimer 10 (4%). At a higher thermolysis temperature (650°), the spiro ketone 3 was found to be unstable, affording the retro‐Diels‐Alder fragments 4‐methylidene‐2‐cyclopentenone (12) (33%) and isoprene (32%). A further example of the influence of an isolated double bond on the yield of the cyclopentenone‐formation sequence A→C was provided by the comparison of the annelation 14→20 (5% overall with Pd(II)‐catalysed acylation) with that of its non‐olefinic analogue 17→21 (53% overall with Friedel‐Crafts acylation).