Configuration sulfoxide groups

The stereochemical course of the enantioface differentiation on the aldehyde is dictated by the configuration of the sulfoxide group sulfinyl-subsdtuted dihydroisoxazoles epimeric at C-5 (e.g., 18) provide aldol adducts 19 with the same configuration at the hydroxy-substituted carbon (C-2 ) independent of the absolute configuration at C-5, however, with different degrees of stereoselectivity23. 

Miscellaneous (formation of complexes, and configuration induced by the sulfoxide group). 

Formation of cyclic sulfoxide (R)-55 by t reatment of bromoarene (i )-54 with tributylstan-nane apparently proves that intramolecular homolytic substitution at the sulfur atom of the sulfoxide group proceeds with strict inversion of configuration (equation 50)103. 

Uemura and coworkers utilized (R)-binaphthol 85 as chiral ligand in place of DET in association with Ti(IV)/TBHP, which not only mediated the oxidation of sulfides to (R)-configurated sulfoxides, but also promoted the kinetic resolution of sulfoxides (equation 50). In this latter process the two enantiomers of the sulfoxide are oxidized to sulfone by the chiral reagent at different rates, with decrease of the chemical yield, but increase of the ee values. Interestingly, the presence of ortho-nilro groups on the binaphthol ligand lead to the reversal of enantioselectivity with formation of the (5 )-configurated sulfoxide. Non-racemic amino triols and simple 1,2-diols have been successfully used as chiral mediators. 

The stronger inductive effect of the sulfoxide group results in preferential a-deprotonation of (Z)-l-(ethylsulfmyl)-2-(ethylthio)ethene which leads to 1-substituted -products 6 via lithiated intermediate 2. Additionally small amounts of 2-substituted products 7 are formed via intermediate 3 due to /1-dcprotonation. Temperature dependent experiments demonstrate that a-lithi-ated Z-intermediate 2 is configurationally labile and is in equilibrium with the corresponding -intermediate which leads to products 5. 

In the case of the (5,/ )-3-hydroxy sulfoxide, the OH group has to be protected by a trifluoroacetyl group before hydroxylation, which was highly stereoselective and fully controlled by the chiral sulfoxide group. Very similar results were obtained in the case of allylic 3-hydroxy sulfoxides having a (Z)-geometry on the double bond. Trihydroxy sulfoxides in all possible configurations can therefore be made by this method (Scheme 60). 

Michael addition of scalemic /3-ketosulfoxides R1COCH2S (0)To1 (chiral at sulfur) to O, /3-unsaturated aldehydes R CH=CHCHO, catalysed by proline derivatives, has been shown to exhibit complete control of configuration at the two newly constructed chiral centres. The configuration at the a-position of the moiety originating from the nucleophile is controlled by the sulfoxide group, whereas the configuration at the -position of the Michael acceptor is controlled by the catalyst, which allows the preparation of all possible diastereoisomers in an enantiomericaUy pure form. Theoretical calculations suggest that enolates, rather than enols, are the active reactants. " ... 

For these authors an OA sulfoxide would be an interesting co-monomer to induce asymmetry into the backbone of a polymeric chain but this is not very clear again. Comparison of ORD and CD curves of the model Xc and of the copolymer Xa indicates that copolymerization occurs with retention of configuration of the sulfur atom and that the sulfoxide group does not lose its configuration when adjacent to a carbanion. 

Lithium A number of Michael-type additions of organolithiums have been described. This is also the case of the reaction of aryllithiums with nitroalkene (389). Deprotonation of the benzylic fluoride (455) with LDA, directed by the neighbouring sulfoxide group, generated the benzyllithium intermediate (456), which underwent addition to the Michael acceptor R CH=CHY (Y = CO2BU, S02Ph R = Ar, alkyl, alkenyl) in a diastereoselective manner controlled by the chiral sulfur to afford the 5yn-configured product (457) with <99 1 dr ... 

Finally, since besides the inductive effect of the sulfoxide and the sulfone functional groups, hydrogen bonding, field effects and steric effects to solvation may or may not work in the same direction, the pKx values can be useful in assigning configurations of suitable pairs of stereoisomeric sulfoxide and sulfone carboxylic acids291. 

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