Diels-Alder reaction of R-(-)-carvone with isoprene

Diets-Alder reactions of R-(-)-carvone with isoprene using different Lewis acids as catalysts have been studied. The best results were obtained with E tAlCl2 at 25 degrees C for 48 hours. The yields are quantitative and the d. e. is 86.8%. Regioselective dihydroxylation at the endocyclic double bond o f the cycloadduct followed by acetonation gave a crystalline acetonide, the structure and stereochemistry of which were confirmed by an X-ray crystall ographic analysis. Hence the stereochemical outcome of the Diels-Alder reac tion is now established and the reaction occurred preponderantly in an anti orientation with respect to the isopropylene group in R-(-)carvone. (C) 19 99 Elsevier Science Ltd. All rights reserved.