1‐Oxo‐1,3‐dithiolanes—synthesis and stereochemistry

1‐Oxo‐1,3‐dithiolane (4) and its cis ‐ and trans ‐2‐methyl (5,6), ‐4‐methyl (7,8) and ‐5‐methyl (9,10) derivatives were prepared by oxidizing the corresponding 1,3‐dithiolanes (1–3) with NaIO 4 in water. The oxides were purified and their isomers separated using thin layer chromatography. The structural characterization was carried out with 1 H and 13 C NMR spectroscopy and molecular modelling. The sulfoxides 4–6 and 8–10 attain two S(1) type envelopes (sometimes slightly distorted) the SO ax envelope greatly dominating. Cis ‐4‐methyl‐1‐oxo‐1,3‐dithiolane is a special case exhibiting both two closely related SO ax (30 and 27%) as well as SO eq (21 and 22%) forms [S(1) and C(4) envelopes, respectively]. The relative energies of these conformations, the values of 1 H‐ 1 H coupling constants and 1 H and 13 C chemical shifts were estimated by computational methods and they support well the conclusions based on the experimental data. Copyright © 2011 John Wiley & Sons, Ltd.