Synthesis of 2-alkylidenecyclopentanones via palladium-catalyzed cross-coupling of 1-(1-Alkynyl)cyclobutanols and aryl or vinylic halides

The palladium-catalyzed cross-coupling of aryl or vinylic halides and 1-(1-alkynyl)cyclobutanols affords good yields of stereoisomerically pure 2-arylidene- or 2-(2-alkenylidene)cyclopentanones, respectively, by a process involving (1) oxidative addition of the organic iodide to Pd(0), (2) carbopalladation of the triple bond of the 1-(1-alkynyl)cyclobutanol, (3) regio- and stereoselective ring expansion to form a novel palladiacycle, and (4) reductive elimination to the 2-alkylidenecyclopentanone with simultaneous regeneration of the Pd(0) catalyst.