Stereospecific synthesis and hydrolysis of optically active diaryl(acylamino)(acyloxy)spiro-λ4-sulfanes and related cyclic diaryl(acylamino)sulfonium salts

Article abstract of DOI:10.1016/S0957-4166(01)00113-6

The stereospecific synthesis of diaryl(acylamino)(acyloxy)spiro-λ⁴-sulfanes (S)-(+)-2, (R)-(+)-5, (S)-(+)-8, and their conversion into related diaryl(acylamino)sulfonium tetrafluoroborates (R)-(+)-3, (S)-(+)-6, (R)-(+)-9, respectively, is described. The enantiomers of spiro-λ⁴-sulfanes (S)-(+)-2, (R)-(+)-5 and (S)-(+)-8 were prepared by dehydration of the corresponding optically active sulfoxide-carboxylic acids (R)-(+)-1, (R)-(-)-4 and (S)-(+)-7, respectively, which were obtained from the racemic forms by diastereoisomeric salt separation with homochiral organic bases. The stereomechanism of the hydrolysis reaction of spiro-λ⁴-sulfanes and sulfonium tetrafluoroborates that depends on pH, the nature of the axial heteroatom, the size of the spiro rings and carboxyl neighbouring group participation is also discussed.