ASYMMETRIC REACTIONS OF THIOACETALS AND THEIR S-OXIDES DERIVED FROM 1,1'-BINAPHTHALENE-2,2'-DITHIOL

The chiral dithiepine 3 was selectively oxidized to all possible oxides: the sulfoxide 9, the sulfone 16, the sulfone-sulfoxide 20, the disulfoxide 21, and the disulfone 22. The sulfinyl oxygens of 9, 14, 20, and 21 are always in the pseudoaxial configuration, as shown by the X-ray structure determination of 11a. Reaction of the anions of 3, 9, and 16 with methyl iodide, benzaldehyde, or acetophenone occurs efficiently. The stereoselectivity of the processes is high and maximized in sulfoxide 9, where the contributions of the chiral binaphthyl residue and the sulfoxide appear to occur synergistically. The alcohols derived from reaction of the anions of 3, 9, and 16 with benzaldehyde and acetophenone were also prepared in high yield and stereoselectivity via reduction or methylation of the phenyl ketone 8 and of its oxidized homologues 14 and 19. Alcohol 6a, prepared in 8:2 ratio in the reaction of 3 with benzaldehyde, was obtained as a single diastereoisomer in the reduction of 8 with lithium aluminum hydride.