Lewis Acid Catalyzed Geminal Acylation Reaction of Ketones with 1,2-Bis[(trimethylsilyl)oxy]cyclobutene: Direct Formation of 2,2-Disubstituted 1,3-Cyclopentanediones

Ketones reacted with 1,2-bis((trimethylsilyl)oxy)cyclobutene (1) under catalysis by boron trifluoride etherate to yield 2,2-disubstituted 1,3-cyclopentanedione products via silylated cyclobutanone intermediates in a two-step, one-pot process. In many instances addition of a small amount of water to the reaction medium after completion of the first step assisted the subsequent rearrangement to the product, such that reversion of the intermediate to the starting ketone became an insignificant process. Yields were best with cyclohexanones (>90%), but steric hindrance and conjugated double bonds reduced yields considerably.