The enantiomers of the cyclic thiolsulfinate naphtho[1,8-cd]-1,2-dithiole 1-oxide, (+/-)-1, have been obtained by semipreparative chiral liquid chromatography of the racemate and characterized by chiroptical methods. The inherent dissymmetry of the extended chromophore gives rise to a very high specific rotation (>1500 in CH2Cl2 at 546 nm). The enantiomers of the corresponding sulfoxide, 2H-naphtho[1,8-bc]thiophene 1-oxide (+/-)-2, showed the chiroptical behaviour expected for an aryl alkyl sulfoxide. CD spectra of 1 and 2 were completely different and could not be used to determine their relative configuration, showing the large effect from substituting S for CH2 on the electronic transitions in the system. The racemization of (+)-1 was studied at 80 degrees C and the rate was found to be increasing rapidly with increasing polarity of the solvent, being 55 times higher in water than in 1-propanol.
This work was supported by grants from the Swedish Natural Science Research Council (K-AA KU 02508-323) and from the Knut and Alice Wallenberg Foundation.