Trimethylsilyl triflate catalysed diels-alder reaction of TMS ethers of conjugated dienols with cyclic enones : evidence for an endo transition state, and first application to synthesis of enantiopure octalins

Although the Diels-Alder (DA) reaction of 2-cyclohexenones and 1,3-dienes is in principle an elegant method of synthesizing decalin systems, the thermal reaction proceeds poorly. In 1960, it was noted that Lewis acid catalysts increase the rate, and enhance yield and stereoselectivity of the reaction. It is generally accepted that the concerted cycloaddition mechanism still applies . When the π-faces of either reactant are diastereotopic, diastereoisomers arising via addition syn or anti to the group that renders the face diastereotopic are formed. Syn selectivity is particularly prevalent in 6-alkyl cyclohexenones.