The Asymmetric Diels–Alder Cycloaddition Using Ethyl (−)-(Z)-(R)S-2-Methyl-3-(p-tolylsulfinyl)propenoate: Application to an Enantioselective Synthesis of (+)-epi-β-Santalene

The Diels–Alder reaction of ethyl (−)-(Z)-(R)S-2-methyl-3-(p-tolylsulfinyl)propenoate (6) with cyclopentadiene gave the cycloadducts 7, 8, and 9 in a high diastereoselective manner. The cycloadduct 7 was transformed into the acetal (−)-25. The racemic 25 was used as an intermediate in the synthesis of (±)-β-santalol. Thus, the chiral acetal (−)-25 should provide a route to (−)-β-santalol. The cycloadduct 8 was converted into (+)-epi-β-santalene in 11 steps.