Total Synthesis of dl-Chamaecynone a Termiticidal Norsesquiterpene

The total synthesis of dl-chamaecynone (1), which has termiticidal activity, has been accomplished. The key compound (30a), which has the same four chiral centers as chamaecynone (1), was obtained in a single step by taking advantage of the Diels-Alder reaction of 5-ethynyl-2-methylcyclohex-2-en-1-one (3) with 1-methoxy-3-trimethylsiloxy-1,3- pentadiene (4). The stereostructure of the major adduct of the Diels-Alder reaction was determined to be the formula (30a) by INDOR experiment. The compound (30a) was converted in four steps into dl-chamaecynone. The preliminary examinations of the Diels-Alder reaction of trans-1-methoxy-3-trimethylsiloxy-1,3-butadiene (2) with 1-carvone and the compound (3) were also carried out, respectively.