| Abstract
| - BF3·Et2O-catalyzed geminalacylation of ketones and acetals with3-methyl-1,2-bis[(trimethylsilyl)oxy)]cyclobutene (3) provided methylcyclopentanedionesin yields that ranged from 40 to 94%.The best substrates were unhindered cyclohexanones. Withacetals, stereochemical preferencesin the initial Mukaiyama-like aldol step giving cyclobutanonestranslated into the stereochemistryof the ultimate cyclopentanedione products. With ketones,equilibration of the initial cyclobutanonecompounds resulted in cyclopentanedione products with a differentstereochemical preference. Thegem-dimethylcyclobutene reagent 4 reacted withketones to give gem-dimethylcyclopentanedionesin modest yield. The process was much more stereochemicallyefficient than the reaction with 3.Rearrangement from the initial cyclobutanone compound waspartially diverted toward air-sensitive3-furanone compounds and ring-opened 1,2-diones. Only furanones(e.g., 52 and 53) were isolatedfrom reactions with the tetramethylcyclobutene51.
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