Asymmetric synthesis and applications of chiral 3-phenylsulfinyl-3-sulfolenes

The chiral 3-phenylsulfinyl-3-sulfolene 2 (S-form) was efficiently prepared in 92% ee by oxidation of sulfide 1 with Ti(O-i-Pr)4/(−)-DET/t-BuOOH (1:4:1) in toluene. Thermal desulfonylation of 2 gave chiral diene 3. Deprotonation of 2 by BuLi followed by the reaction with alkyl halides gave regiospecifically the C-2 alkylated 3-sulfolenes 4–8. Intramolecular Diels–Alder reactions of compounds 7 and 8 gave the bicyclic products 9–11. Thermal desulfonylation of 4 generated chiral dienyl sulfoxide 15, which underwent thermal and Lewis acid-catalyzed Diels–Alder reactions with good regio-, stereo- and enantioselectivity.