Diastereoselective Synthesis of Tetrahydrofurans from Aryl 3-Chloropropylsulfoxides and Aldehydes

Carbanions of aryl 3-chloropropylsulfoxides react with nonenolizable aldehydes to give 2,3-disubstituted tetrahydrofurans. Deprotonation of the sulfoxides carried out in the presence of aldehydes results in the addition of the carbanions to the carbonyl group of the aldehydes, followed by 1,5-intramolecular substitution of the resulting aldol-type anion to produce the tetrahydrofuran ring. The 2-aryl and 3-arylsulfinyl substituents are always in trans relation, and the reaction proceeds with high diastereoselectivity also in respect to the chiral sulfur atom. The diastereoselectivity is attributed to the cyclic transition state of the aldol addition and increases when the aromatic ring of the sulfoxide contains electron-withdrawing substituents, whereas that of the aldehyde has electron-donating groups.