1,3,2-Dioxathiolane 2,2-dioxide

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

Significant advances in the chemistry of these ring systems over the past 10 years include the first unambiguous detection, and characterization by microwave spectroscopy as 1,2,3-trioxolane, of the primary ozonide from ethene and ozone (cf. Section 4.15.3.2), and the introduction of 1,3,2-dioxathiolane 2,2-dioxides as epoxide equivalents in organic synthesis (cf. Section 4.15.5.3). Advances have also been made in the synthesis and characterization of the chemistry of 1,2,3-trithiolanes and 1,2,3-trithioles. 

The gas-phase dipole moment of 1,2,3-trioxolane was determined to be 3.43 D from microwave spectroscopic studies <88JA799l>. This compares with calculated values of 3.90 D and 4.03 D using SCF and MP2 methods, respectively <89JA2497>. The dipole moment of 1,3,2-dioxathiolane 2-oxide has been measured as 3.65 D <49DOK(69)4i> and 3.74 D <6IJA2105> (both in benzene), and that of 1,3,2-dioxathiolane 2,2-dioxide has been determined to be 5.64 D (in dioxane) <68JHC289>. These results are consistent with the compounds adopting nonplanar conformations. 

Dioxathiolane 2,2-dioxide (21) adopts a puckered conformation in the solid state, as shown by x-ray diffraction (Section 4.15.3.1). In solution, the H NMR spectrum of (21) indicates that the compound undergoes a rapid pseudorotation between twist-envelope forms (Section 4.15.3.3.1) the O NMR spectra of simple derivatives also indicate a rapid conformational equilibrium by pscudorotation, although substitution may act as a barrier to complete ring inversion (Section 4.15.3.3.3). The solution-phase dipole moment of 1,3,2-dioxathiolane 2,2-dioxide is consistent with a nonplanar conformation (Section 4.15.3.8). 

In contrast to 1,3,2-dioxathiolane 2-oxides, the hydrolysis of 1,3,2-dioxathiolane 2,2-dioxides proceeds predominantly by nucleophilic attack at carbon, except under strongly alkaline conditions when a small amount of S—O bond fission is also observed . 1,3,2-Dioxothiolane... 

Scheme 21) (92TL5597>. In cases where EjZ isomers of the product alkene are possible, the thermodynamically preferred isomer predominates <90SL479>. Electrochemical reduction of certain 1,3,2-dioxathiolane 2,2-dioxides also affords alkenes <84BCJ3160>. Reduction of the cis and trans isomers of 4,5-dimethyl-1,3,2-dioxathiolane 2-thione using Raney nickel afforded meso- and ( + )-2,3-butanediol, respectively <65JOC2696>. 

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