Deconjugation of α,β-unsaturated esters and an intramolecular Michael reaction of bis-α,β-unsaturated esters with trialkylsilyl trifluoromethanesulfonate in the presence of tertiary amine: synthesis of (±)-ricciocarpin A

Abstract

Treatment of the α,β-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-α,β-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.