The first spontaneous resolution of a sulfoxide: Dianin's compound analogue, (R)-4-(4-hy-droxy-phen-yl)-2,2,4-tri-methyl-thia-chroman-1-oxide.

The title sulfoxide, C18H20O2S, was prepared by controlled oxidation of thia-Dianin's compound using hydrogen peroxide in glacial acetic acid. On recrystallization from glacial acetic acid, it was found to form unsolvated, spontaneously resolved crystals, the initial crystal structure analysis revealing the presence of both sulfoxide epimers in the crystal. On multiple recrystallization a single epimer was observed, with crystallization occurring in the unchanged ortho-rhom-bic space group P212121, with Z' = 1. The mol-ecule possesses a distal conformation, referring to the juxtaposition of the p-hydoxyphenyl substituent with respect to its syn-related methyl group, with the sulfoxide oxygen atom anti to the aromatic substituent. The mol-ecular packing features O-H⋯O hydrogen bond chains running parallel to the b axis of the unit cell.