FIRST DIELS-ALDER REACTIONS OF ENANTIOMERICALLY PURE 1-P-TOLYLSULFINYL DIENES - STRAIGHTFORWARD ACCESS TO CYCLOHEXENOLS THROUGH TANDEM CYCLOADDITION [2,3]-SIGMATROPIC REARRANGEMENT

The asymmetric Diels-Alder reactions of (R)-1-(p-tolylsulfinyl)-1,3-butadienes 3a-c with N-methylmaleimide (NMM) have been explored. The cycloadditions are stereospecific: only one endo adduct is formed, the pi-facial diastereoselectivity being controlled by the sulfoxide both in thermal and catalytic conditions. The in situ cycloaddition/sulfoxide sulfenate [2,3]-sigmatropic rearrange ment starting from chiral 3a-e in the presence of an excess of NMM, which acts as thiophilic agent, provides a convenient one-step access to enantiomerically pure and all-cis functionalized cyclohexenols (-)-5a-c.