An efficient synthesis of α-substituted α,β-unsaturated ketones employing a versatile latent α-ketovinyl anion equivalent

✍ Scribed by Michael A. Guaciaro; Peter M. Wovkulich; Anos B. Smith III

• Book ID: 104237342
• Publisher: Elsevier Science
• Year: 1978
• Tongue: French
• Weight: 226 KB
• Volume: 19
• Category: Article
• ISSN: 0040-4039
• DOI: 10.1016/s0040-4039(01)85698-7

✦ Synopsis

In connection with our synthetic program directed at the elaboration of cyclopentenoid antibiotics we required an efficient method for the construction of a variety of a-substituted a,B-unsaturated ketones directly from the parent enone (i.e. 1+2), which did not require intervention of the thermodynamic dienolate. To our _ _ knowledge a general solution for this recurring synthetic problem is unavailable,

."-___e.. although Corey, 1 Fuchs' and Stork3 have independently developed a reverse polarity (umpolung) strategy for a-alkylation and a-arylation of a,B-unsaturated ketones. Central to their approach was the generation of an effective latent equivalent for aketovinyl cation 3. Such a strategy, however, is limited in that it depends critically upon the availability of the requisite alkyl or aryl organocuprate or magnesium reagent. t 0 0 I -fjE &J 1 2 3 4 a-Ketovinyl a-Ketovinyl cation anion A more versatile and possibly more direct approach for the conversion of 1 to ,2, albeit hypothetical, would be the generation of a-ketovinyl anion 4, followed by addition of an appropriate electrophile. 4 While the generation of such an anion, per se, *..,_ ___ is not feasible, recent studies by Picini, 5a HouseSb and Swenton5c suggest that a-bromoketal 5 could serve as a viable latent equivalent of 4, providing the following criteria could be met successfully: a) metalation of 5; b) electrophilic -* 9