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

Abstract The stereospecific synthesis of diaryl(acylamino)(acyloxy)spiro-λ 4 -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-λ 4 -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-λ 4 -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.