STEREOCHEMISTRY OF THIOXANTHENE SULFOXIDE AND ITS C-9 METHYLATED ANALOGS . CONTROL OF CONFORMATIONAL DISTRIBUTION IN FOLDED MOLECULES BY PERI SUBSTITUTION

Thioxanthene 10-oxide prefers that conformation in deuteriochloroform in which the sulfinyl oxygen atom is pseudoequatorial. Similar behavior has been observed for cis- and trans-9-methylthioxanthene 10-oxides and 9,9-dimethylthioxanthene 10-oxide. 1-Methyl-4-chlorothioxanthene 10-oxide prefers that conformation in which the sulfinyl oxygen atom is pseudoaxial. Equilibration of cis- and trans-9-methylthioxanthene 10-oxide indicates that the trans isomer is the more stable. An initial discussion of the structural similarities and dissimilarities of meso-substituted 9,10-dihydroanthracenes and thioxanthenes is presented. The short wavelength (ca. 210 μm) transitions in the electronic spectra of the isomeric 9-methyl-9-hydroxythioxanthene 10-oxides will allow assignment of configuration to these isomers. However, this technique cannot be applied to the isomeric 9-methylthioxanthene 10-oxides since these transitions occur at ca. 204 mμ in both isomers. © 1969, American Chemical Society. All rights reserved.