Chiral sulfinate groups

C. ALLYLIC DERIVATIVES BEARING CHIRAL SULFINATE GROUPS... 

Zwanenburg and his group [105] have addressed the question of the tautomeric interconversion of aliphatic sulfines into vinyl sulfenic acids. They have synthesised dithioesters bearing an a asymmetric carbon centre. Oxidation with mCPBA did produce chiral sulfines, which did not racemise except when a phenyl group was attached to the a carbon. 

Chiral sulfoxides are conveniently synthesised by Andersen s method (1962), in which a chiral sulfinate (4) is treated with a Grignard reagent. The reaction involves a sulfinyl group transfer and occurs with complete stereochemical inversion at the sulfur atom... 

Recently Ribeiro et al. [65] reported on the synthesis and characterization of a variety of tolanes that had optically active sulfinate groups. Some of these compounds, see 23, were found to possess a phase that exhibited oily-streak textures typical of chiral nematic phases and also defect pattern associated with columnar phases (the earlier photomicrograph Plate 6 for 14P1M7 is similar). 

Higher enantioselectivities were reported by Sun et al. by using a chiral bissulfinamide with a polymethylene tether coimecting the two chiral sulfin-amide functional groups for similar reactions." At a catalyst loading of 10 mol %, a wide variety of chiral amines were obtained in high yields and enantioselectivities of up to 96% ee (Scheme 8.2). Furthermore, these authors also... 

Clayden s group has reported pioneering studies on asymmetric ortho-lithiation reactions. They have shown that treatment of lithiated hindered tertiary amides such as 19 with chiral sulfinate esters of type 20 gives the... 

Complete asymmetric induction is observed in the cycloaddition reaction of 2,3-dimethyl-1,3-butadiene with chiral camphor or sulfoximino substituted sulfines . Excellent yields are obtained for the cycloaddition reaction of sulfoximino sulfines which have the inducing chiral center in close proximity to the sulfine group. 

Chiral sulfoxides are useful intermediates in asymmetric synthesis. A number of methods for their preparation were developed in the last decade. An interesting displacement of dimethylphosphonylmethyl moiety, a carbon leaving group, from sulfur by Grignard reagents was used to obtain enantiomerically purep-tolyl sulfoxides.3 4 Optically pure methyl 4-bromophenyl sulfinate was subjected to a one-pot sequence yielding unsymmetrical dialkyl sulfoxides in 60-97% yield and >98% ee. A simple one-pot synthesis of chiral sulfoxides from norephedrine-derived... 

This is the second important contribution of Kagan s group in the synthesis of chiral sulfoxides. The method was reported in 1989 for the synthesis of tert-butyl sulfoxides,90 and the full paper on the generalization of the method was published in 1991.86 The approach is based on the synthesis and use of an o.p. cyclic sulfite in the synthesis of various sulfoxides by two successive condensations of two organometallic reagents, RjM and R2M. Thus, the sulfoxides are produced in three separate steps the formation of cyclic sulfite, synthesis of sulfinate esters, and transformation of sulfinates to chiral sulfoxides. 

However, this method suffers severely from the tedious experimental conditions leading to the sulfoxides from diol 52. Several crystallizations are required—the first to purify the tnms sulfite, a second to purify the hydroxy sulfinate, and, finally, a column chromatography to purify the sulfoxide. This may be the reason why there is no application of this method in the literature, apart from that by the same group in the sulfinylation of ferrocene,94 getting the o-lithium derivative to react with various electrophiles to afford chiral ferrocenes (Scheme 17,59 R = HOCMe2, Me, Ph2P). 

In a competition experiment between chiral N-sulfinyl oxazolidinone and Andersen s menthyl sulfinate ester, it has been shown that the former is at least two orders of magnitude more reactive than the latter. This finding is being used to avoid some of the problems involved in sulfinate esters, related to the nature of the alkoxide leaving group in the nucleophilic substitution. 

The rearrangement of unsymmetrically substituted allylic sulfinates involves simultaneous isomerization of the allylic group. Full inversion of configuration is observed in the conversion of (4/0-4-(2,4-dimethylphenylsulfinyIoxy)-2-pentene to the (4S)-product l131. This conversion is also the first example of a C - C 1,3-chirality transfer accompanied by C—S bond formation. 

As expected for this mechanism, the reactivity falls off as the alkyl group becomes more bulky and as the substituents become more electron-attracting. By carrying out a crossover reaction on a mixture of RS and SR isomers of [CpFe (CO)L CH2C H(Me)Ph ], which is chiral at both Fe and the carbon shown, very little of the crossover products, the R,R and 5,5 isomers of the sulfinate complex, are seen. This shows that the postulated ion pairs must stay together, and that the intermediate iron cation also has stereochemical stability. Ion pairing is very common in organic solvents, and the ions probably rarely break free from the ion pair- "... 

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