Dithiolanes, asymmetric oxidation

Dithiolane oxides, synthesis of 241 Dithiolanes, asymmetric oxidation of 291 Divinyl sulphones, reactions of 642, 1021 Divinyl sulphoxides reactions of 349, 352, 353, 359 synthesis of 240 Donor-acceptor capacities 387... 

The modified Sharpless reagent was also successfully applied288 for the asymmetric oxidation of a series of 1,3-dithiolanes 248 to their S-monooxides 249 (equation 134). It was observed that the optical induction on sulphur (e.e. from 68 to 83%) is not significantly affected by the substituents R1 and R2. Asymmetric oxidation of a few aryl methyl sulphides by organic hydroperoxides in the presence of a catalytic amount of the optically active Schiff base-oxovanadium(IV) complexes gave the corresponding sulphoxides with e.e. lower than 40%289. 

The procedure with an excess of DET gives better results in the asymmetric oxidation of 1,3-dithiolane (Table 9). This latter finding has been elegantly applied by the same group to the resolution of racemic ketones, through their transformation into 1,3-dithiolanes, asymmetric monosulfoxidation followed by diastereomeric separation, and regeneration of the parent ketone.56... 

Optically active 1,3-dithiolane monooxides serve as chiral masked acyl groups. Although, numerous methods have been reported for oxidation of racemic 2-substituted-l,3-dithiolanes, asymmetric syntheses were not known. 

A number of anionic systems that are related to 1,3-dithian have been studied, including the anion from the unusual 1,3-oxathian (37) [which has been employed with excellent results in an asymmetric synthesisl, the 1,3-dithiolan anion (38) [which reacts with trialkyIboranes (as well as with other electrophiles) to give, after oxidative work-up, ketones or tertiary alcohols (39), as shown in Scheme 3], and 2-substituted 1,3-dithiolan anions [which fragment to give aromatic dithioestersl (see Chap. 3, Pt III, p. 191). 

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