ENANTIOSELECTIVE DIELS-ALDER CYCLOADDITIONS WITH (SS)-2-(P-TOLYLSULFINYL)-1,4-NAPHTHOQUINONE - EFFICIENT KINETIC RESOLUTION OF CHIRAL RACEMIC VINYLCYCLOHEXENES

Chiral racemic vinylcyclohexenes 1a-m, bearing allylic and nonallylic oxygenated substituents on the cyclohexene ring, were submitted to Die ls-Alder reactions with enantiomerically pure (SS)(2-p-tolylsulfinyl)- 1,4-naphthoquinone. The tandem cycloaddition/pyrolytic sulfoxide elimi nation led to the formation of enantiomerically enriched angularly tet racyclic quinones (+)-8a and (+)-12, arising from the kinetic resoluti on of the racemic diene. Dienes la-c, bearing an alkoxy substituent at the allylic position C-3, and 1d-g, with C-3 alkoxy and C-5 methyl gr oups, gave exclusively quinones (+)-8a-g, resulting from the anti appr oach to the dienophile. A similar anti selectivity occurred in cycload ditions of dienes 1ij, viith the alkoxy group situated at the allylic position C-6. Nonallylic 4-substituted vinylcyclohexenes 1k-m evolved to ca. 75:25 mixtures of (+)-anti-8k-m and (+)-syn-12k-m derivatives. In all cases, (SS)-(2-p-tolylsulfinyl)-1,4-naphthoquinone reacted from the less hindered face of the more reactive s-cis conformation, givin g rise to products in moderate to excellent enantiomeric excesses. Ste ric effects and torsional interactions in the corresponding approaches account for the observed pi-facial diastereoselectivities at both par tners.