DECONJUGATION OF ALPHA,BETA-UNSATURATED ESTERS AND AN INTRAMOLECULAR MICHAEL REACTION OF BIS-ALPHA,BETA-UNSATURATED ESTERS WITH TRIALKYLSILYL TRIFLUOROMETHANESULFONATE IN THE PRESENCE OF TERTIARY AMINE - SYNTHESIS OF (PLUS-OR-MINUS)-RICCIOCARPIN-A

Treatment of the alpha,beta-unsaturated esters 1, 6 and 8 with trialkylsilyl trifluoromethanesulfonate in the presence of a tertiary amine gave, via silyl dienol ethers, the corresponding deconjugated esters 3, 7 and 9 as the major products, respectively. Reaction of bis-alpha,beta-unsaturated esters 12a and 12b with a trialkylsilyl trifluoromethansulfonate in the presence of a tertiary amine caused an intramolecular Michael reaction to produce the cyclopentanes 14a and 20a and the cyclohexanes 14b and 20b. Bicyclic compounds 21a and 21b formed by tandem Michael-Dieckmann or intramolecular Diels-Alder reaction were concurrently obtained. The cyclohexane derivative 14b was converted into the racemate of a sesquiterpene, (+/-)-ricciocarpin A 22.