Exciton coupling in the CD spectra of chiral spiro-lambda(4)-sulfanes and related sulfonium salts

Enantiomers of spiro-lambda (4)-sulfanes 2-7 and related cyclic sulfonium s alts 2c-7e have been obtained by stereospecific synthesis. Exciton splittin g was observed in the CD spectra of spiro-lambda (4)-sulfanes and sulfonium salts having both benzene and naphthalene-benzene rings. The absolute conf igurations were deduced from the sign of the coupler. Exciton couplets in t he CD spectra of sulfonium salts and their parent lambda (4)-sulfanes show the same sign which follows from the same orientation of the coupled electr ic transition moments due to their similar trigonal bipyramidal geometry. B ased on the known stereomechanism of the formation of spiro-lambda (4)-sulf anes and sulfonium salts as well as of their hydrolysis leading to the corr esponding sulfoxides (2a-7a and 2b-7b), the absolute configurations of sulf oxides could also be deduced from the sign of exciton coupler in the CD spe ctra of related lambda (4)-sulfanes and sulfonium salts.