A CONVENIENT PREPARATION OF 3-ALKYLCYCLOPENTENONES FROM ALKYLCYCLOPENTADIENES

Improved syntheses of cyclopentenones are being continually developed, in part, because alkylated cyclopentenones have figured prominently in synthetic approaches to, for example, triquinane and prostaglandin natural products.2 Existing approaches to 3-alkylcyclopentenones 5, one of the more important types of these compounds, are numerous and include, inter alia, Pauson-Khand and Nazarov type cyclizations and intramolecular aldol condensations.3-5 In connection with other ongoing projects we needed to prepare a variety of these compounds on a large scale in an efficient manner. Most existing methods for the synthesis of these compounds require expensive starting materials, are inefficient, or involve conditions not compatible with certain functional groups. We report here a three-step sequence to compounds 5 from alkylcyclopentadienes 1, which seems broadly applicable to the synthesis of these compounds. © 1990, American Chemical Society. All rights reserved.