An Efficient Procedure for the Preparation of (<i>E</i>)-α-Alkylidenecycloalkanones Mediated by a CeCl₃·7H₂O−NaI System. Novel Methodology for the Synthesis of (<i>S</i>)-(−)-Pulegone¹

Abstract

2-Alkylidenecycloalkanones are powerful synthons used as the key intermediates in many important syntheses. Because of their potential, a general method of preparation from readily available starting materials, under very mild conditions, was considered to be worthwhile. Cerium(III) chloride heptahydrate in combination with sodium iodide in refluxing acetonitrile promotes a regio- and stereoselective beta-elimination reaction to (E)-2-alkylidenecycloalkanones in 2-(1-hydroxyalkyl)cycloalkanones. The synthetic value of the present procedure is demonstrated by the synthesis of monoterpene (S)-(-)-pulegone (8) in its optically active form.