Chiral sulfur compounds. Part 25. Diastereoselective 1,2-additions of lithiated (+)-(S)-N-tert-butyldiphenylsilyl-S-methyl-S-phenylsulfoximine to ketones

Lithiated (+)-(S)-N-tert-butyldiphenylsilyl-S-methyl-S-phenylsulfoximine 2f reacts with prochiral ketones to give a mixture of diastereoisomeric β-hydroxy sulfoximine adducts with a diastereoselection ranging from 79:21 to 98:2 depending upon the steric demand of the ketone. Racemic Chiral cyclic ketones react with 2f to give a mixture of diastereoisomeric β-hydroxy sulfoximine adducts which could be separated by a combination of column chromatography and recrystallization. Thermolysis of the diastereoisomerically pure adducts gave 2-alkylcyclohexanones in high enantiomeric purity. The relative stereochemistries of four of the β-hydroxy sulfoximine adducts have been unequivocally determined from single-crystal X-ray structural analysis. The stereochemical outcome of these 1,2-additions can best be rationalized by invoking competing boat transition states.