Studies of diastereoselectivity in Diels-Alder reactions of enantiopure (SS)-2-(p-tolylsulfinyl)-1,4-naphthoquinone and chiral racemic acyclic dienes

Enantiopure sulfinylnaphthoquinone (+)-5 reacted with racemic acyclic diene s 1a-f bearing a stereogenic allylic center, through a tandem cycloaddition /pyrolytic sulfoxide elimination, to afford optically enriched compounds 8a -f and 9a-f with good like/unlike selectivities (ca. 75:25) and good enanti omeric excesses (68-82%), arising from the partial kinetic resolution of th e racemic dienes. The opposite diastereoselection (8g-i: 9g-i, up to 5:95) was observed in reactions with dienes 1g-i, having an additional methyl gro up at C-3, the enantiomeric purities being moderate (14-25%). Steric effect s and torsional interactions in the corresponding approaches account for th e observed diastereoselectivities.