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

[GRAPHICS] The palladium-catalyzed cross-coupling of aryl or vinylic halides and 1-(1- alkynyl)cyclobutanols affords good yields of stereoisomerically pure 5-aryl idene- or 2-(2-alkenylidene)cyclopentanones, respectively, by a process inv olving (1) oxidative addition of the organic iodide to Pd(0), (2) carbopall adation of the triple bond of the 1-(1-alkynyl)cyclobutanol, (3) regio- and stereoselective ring expansion to form a novel palladiacycle, and (4) redu ctive elimination to the 2-alkylidenecyclopentanone with simultaneous regen eration of the Pd(0) catalyst.