C8K-Promoted Self-Condensation and Self-Condensation-Cycloisomerization Reactions of α,β-Unsaturated Fischer Carbene Complexes

✍ Scribed by Miguel A. Sierra; Pedro Ramírez-López; Mar Gómez-Gallego; Tore Lejon; María José Mancheño

• Publisher: John Wiley and Sons
• Year: 2002
• Tongue: English
• Weight: 99 KB
• Volume: 41
• Category: Article
• ISSN: 0044-8249
• DOI: 10.1002/1521-3773(20020916)41:18<3442::aid-anie3442>3.0.co;2-z

✦ Synopsis

The chemistry of stabilized Group 6 metal carbene complexes (Fischer carbenes) has reached a high level of maturity and carbenes have become very valuable building blocks in organic synthesis. In spite of this, the reactivity of highly reduced Fischer carbene complexes has been somewhat neglected. The one-electron reduction of the Group 6 alkoxyaryl carbene complexes 1 by Na/K alloy was originally reported by Casey. In this case, radical anion species 2 stable in diluted THF/hexamethyl phosphoramide (HMPA) solutions were detected by ESR spectroscopy. Further, Cooper and Lee reported the reaction of [Bu 3 P(CO) 4 CrC(OMe)Ph] (3), with potassium 1-methylnaphthalenide to yield the highly reduced carbene complex 4 2À (Scheme 1). This species 4 2À shows the expected umpolung at the carbene carbon atom (which becomes a nucleophile as a result of the increased COMMUNICATIONS 3442