Adaption of Oxyanionic Sigmatropy to the Convergent Enantioselective Synthesis of Ambergris-Type Odorants

Article abstract of DOI:10.1021/jo00023a018

(-)-(1S,4R)-5,8,8-Trimethylbicyclo<2.2.2>oct-5-en-2-one has been prepared in high optical purity in order to adapt its β,γ-unsaturated ketone component to an oxy-Cope strategy aimed at several labdane-like tricyclic ethers.Condensation reactions with the dichloro cerate derivatives of 2,3-dihydrofuran and dihydropyran proceeded regioselectively from the less hindered ? surface, thereby setting the stage for anionically accelerated <3,3>sigmatropic shift.The resulting enolate anions are electronically destabilized relative to their tautomers, which are consequentlyformed efficiently.These are captured by reaction with phenylselenenyl chloride.Once selenoxide elimination and reduction with NaBH4-CeCl3 had been accomplished, the stage was set for installation of trans A/B ring stereochemistry.Direct saturation of original dienones led instead to the cis A/B isomers.The enantioselective syntheses were completed by conversion to the respective xanthates and reduction of these intermediates under free-radical conditions.The results indicate that a practical route to certain potent olfactory agents has been developed.