DiTOX substrates

Table 5. Mannich Reaction of Enolates of 2-Propionyl-2-ethyl DiTOX Substrates Using Eschenmoser s Salt as Aminoalkylating Agent...

Asymmetric sulfoxidation of2-acyl-1,3-dithianes Preparation of optically pure DiTOX substrates. The preliminary investigations of 1,3-dithiane derivatives as asymmetric building blocks and chiral auxiliaries described in this review... 

Unless otherwise stated, racemic 2-acyl-2-alkyl-DiTOX derivatives were used as substrates for the applications described in this review. The preparation of enan-tiomerically pure 2-acyl-2-alkyl-DiTOX systems are described in a subsequent section. 

For the syn substrate 8, the approach of the organometallic nucleophile is controlled by the steric bias imposed by the bulky DiTOX ring (Fig. 2). The nucleophile approaches the prochiral carbonyl group from the direction of the... 

Several approaches to the enantioselective oxidation of sulfides have been reported,61 including enzymatic approaches,62 use of optically pure oxidants,63 and several modifications of the Sharpless epoxidation procedure.63,64 The success of these procedures is somewhat substrate dependent for example, dialkyl sulfides and more complex substrates can give unpredictable results. 1,3-Dithiane itself is oxidized with only ca. 20% ee optically pure DiTOX has, however, been obtained by resolution.65... 

Enantiomerically pure DiTOX systems (95) and (96) were used to prepare a-hydroxy acids [132], Page had previously described the stereoselective reduction of 2-acyl-2-alkyl-l,3-dithiane 1-oxides with DIBAL [113], and normally observed [132] a reversal of selectivity upon addition of zinc chloride. In this case (Scheme 4.73), THF solutions of the substrates were treated at -78°C with either DIBAL or DIBAL/ZnCl2 reducing systems. As expected, the DIBAL and DIBAL/ZnClz reducing systems gave products of opposite stereoselectivity in most cases only one product diastereoisomer was observed. 

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