1.3- Dithiane dioxide

Aggarwal has demonstrated the success of a variety of electrophilic reactions involving the C2 symmetric species, 1,3-dithiane dioxide.76a-c This substrate is easily prepared in 60% yield from oxidation of 1,3-dithiane with sodium metaperiodate, and is isolated as a mixture of diastereoisomers in a ratio of 95 5 in favor of the trans-1,3-dithiane-S,S-dioxide product. 

Aggarwal has discovered that the anion derived from 1,3-dithiane dioxide undergoes rapid reaction with a range of aldehydes leading to the formation of diastereoisomeric mixtures in good yield (Scheme 20).76b... 

In the equilibrium mixtures of thiane oxide (2) and 1,3-, 1,4-dithiane dioxides (3) and (4), the axial conformers are present predominantly over the equatorial conformers at low temperatures (— 90 °C). For instance in the monoxide (2) a ratio of 62% axial and 48% equatorial conformers has been observed. The prevalence of the axial conformers in the sulphoxides (2) and (4) has been explained to be due to hydrogen bonds between the oxygen in the axial sulphinyl group and the hydrogen atom at the 3-position as shown in Scheme 7121 127. 

Enantioselective oxidation of 1,3-dithianes to corresponding S-oxides and S,S-dioxides by designer yeast 99JHC1533. 

Hexafluorophosphate derivatives, such as [M(Me2SO)n][PF6]3 (M = La, Lu, Y), have been synthesized (365), and infrared data show O-bonding of the sulfoxide with ionic hexafluorophosphate groups. Analytical data are incomplete for this series, as decomposition, postulated to be to lanthanide fluorides, occurs. The (CH2)4SO complexes [M( CH2 4SO)t.5][PF6]3 are reported (145), which are 3 1 electrolytes with uncoordinated anions, implying a possible semibridged structure, as previously mentioned. Complexes of other cyclic sulfoxides, including thioxane oxide (146) and trans-1,4-dithiane-1,4-dioxide (147) derivatives of hexafluorophosphate salts have also been prepared. 

The enthalpies of combustion, sublimation, and formation of 1,3-dithiane and its 1-oxide (sulfoxide) and 1,1-dioxide (sulfone) have been measured (Table 11) and aA initio MO-calculated at the G2/MP2 level <1999JOC9328, 2004JOC1670, 2004JOC5454> calculated Aff/°n,(g) values agree well with the experimental values. 

Table 11 Standard molar enthalpies of combustion, sublimation, and formation for 1,3-dithiane and its 1 -oxide and 1,1-dioxide at 298.15 K...

Optically active 2-alkylidene-l,3-dithiane 1,3-dioxides have been prepared as chiral Michael-type acceptors. It was shown that these compounds react under nucleophilic epoxidation conditions to give diastereoselectively the epoxides. Other heteroatom nucleophiles reacted as well <1998JOC7128, 1999PS(153/4)337>. It was further demonstrated that enolates were also effective nucleophiles for the stereoselective addition to 2-alkylidene-l,3-dithiane 1,3-dioxides (Scheme 48) <20050L4013>. 

The use of chiral 2-alkylidene-l,3-dithiane 1,3-dioxides in asymmetric cycloaddition reactions has been demonstrated. A highly enantioselective synthesis of (—)-cispentacin by an intramolecular 1,3-dipolar cycloaddition was reported (Scheme 52) <20020L1227, 20030BC684>. 

Oxidation of 1,3-dithianes to 1,3-dithiane 1-oxides has been carried out by various methods using H2O2 or /-butyl hydroperoxide (TBHP) as oxidant. In the presence of chiral co-oxidants, optically active 1,3-dithiane 1-oxides have been prepared (Scheme 66). A compilation of some currently used methods is given in Table 13. The oxidation to 1,3-dithiane 1,3-dioxides was conducted similarly. Sharpless conditions were found to be highly effective with 2-alkyl- or alkylidenyl-substituted substrates. The parent 1,3-dithiane 1,3-dioxide was obtained by basic removal of a 2-carboxyl group in 83% yield and 99% ee <1998JOC7306>. 

Tabie 13 Oxidation of 1,3-dithianes to 1,3-dithiane 1 -oxides or 1, 3-dithiane 1,3-dioxides under various (asymmetric) reaction ... 

A theoretically estimated enthalpy of formation of 1,4-dithiane 1,1-dioxide was calculated from high-level ab initio molecular orbital calculations at the G2(MP2) level. The theoretical calculations appear to be in very good agreement with experiment (enthalpy of formation (T = 298.15 K) of 1,4-dithiane sulfone = —333.0kJ mol ) <2006JOC2581>. 

Measurement of enthalpies of formation in the condensed and gas phase have shown that 1,4-dithiane 1,1-dioxide is 6.7kJmoD more stable than 1,3-dithiane 1,1-dioxide <2006JOC2581>. 

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