Tetramethyl-1,3,2-dioxathiolane 2,2-dioxide

Dioxathiolane 2,2-dioxide, 4,4,5,5-tetramethyl-dipole moment, 6, 865 <77IZV98)... 

Cyclic sulfites and cyclic sulfates of ethanediol undergo hydrolysis with acids to furnish glycol. The substituted cyclic sulfate, such as tetramethyl-1,3,2-dioxathiolane 2-dioxide, may undergo a pinacol type of rearrangement under acidic conditions to furnish pinacolone in good yield (74JOC3415). The mechanistic pathway is rationalized in Scheme 17. 

A similar rearrangement attempted on a five-membered cyclic sulfite failed to yield either a four-membered sulfone or an elimination product. However, tetramethyl-l,3,2-dioxathiolane 2,2-dioxide furnished pinacolone in good yield when heated under aqueous acidic conditions (74JOC3415). In contrast, six-membered cyclic sulfates derived from a number of 1,3-diols underwent a smooth ring contraction reaction when treated with lithium powder and a catalytic amount of 4,4 -di-/ert-butylbiphenyl (DTBB, 5 mol%) in THF at 0°C followed by hydrolysis as shown in Scheme 24 (95T11445). 

---