Asymmetric Sulfur Atoms Research Articles

Stereochemistry controlled by an asymmetric sulfur atom, and a rare example of a kryptoracemate

The ligands 4-methylthio-6-phenyl-2,2'-bipyridine (1) and the corresponding sulfoxide (2) and sulfone (3) have been synthesized and characterized in solution, and in the solid state by single crystal X-ray diffraction. Compounds 2 and 3 crystallize in the same space group (C2/c) with similar unit cell parameters; a small increase in the unit cell volume allows for the presence of the extra oxygen atom in 3. The sulfoxide and sulfone groups adopt conformations that permit intramolecular O···HC(aryl) hydrogen bonds. The complexes [Ir(ppy)(2)L][PF(6)] with L = 1, 2 or 3 have been prepared and characterized. The asymmetric sulfur atom in ligand 2 gives rise to pairs of diastereoisomers of the complex which can be distinguished in the (1)H and (13)C NMR spectra. In solution, exchange of [PF(6)](-) by [Δ-TRISPHAT](-) gives rise to four diastereoisomers and we observed good dispersion of (1)H NMR resonances, especially for those assigned to protons close to the asymmetric sulfur atom. A single crystal X-ray diffraction study of 2{[Ir(ppy)(2)(3)][PF(6)]}·CHCl(3)·3H(2)O reveals that the complex crystallizes in the chiral space group P2(1)2(1)2(1), the asymmetric unit containing crystallographically independent Δ- and Λ-[Ir(ppy)(2)(3)](+) cations. This provides a rare example of a so-called kryptoracemate in the solid state. In MeCN solution, [Ir(ppy)(2)(1)][PF(6)], [Ir(ppy)(2)(2)][PF(6)] and [Ir(ppy)(2)(3)][PF(6)] are weakly emissive (λ(em) = 600, 647 and 672 nm, respectively) and preliminary studies of the electroluminescent properties of [Ir(ppy)(2)(2)][PF(6)] indicate that the complexes are not suitable candidates for LECs.

ChemInform Abstract: Synthesis of (Rc,Ss)-1,1,1-Trifluoro-3-(p-tolylsulfinyl)-2-propanol by an Asymmetric Reduction with a Yeast, Yamadazyma farinosa, as a Key-Step.

(Rc,Ss)-1,1,1-trifluoro-3-(p-tolylsulfinyl)-2-propanol (>99% e.e.), an important reagent for the asymmetric protonation of substituted enolates, was prepared (70%) from (S)-methyl p-tolyl sulfoxide. The stereoselectivity of the Yamdazyma farinosa-catalyzed reduction of carbonyl groups, the key step for the introduction of an asymmetric carbon, was greatly affected by the stereochemistry of the asymmetric sulfur atom. The reduction of (S)-1,1,1-trifluoro-3-(p-tolylsulfinyl)-2-propanone proceeded smoothly and in a quite stereoselective manner to give the desired compound, while a 76 : 24 mixture of (Rc,Rs)- and (Sc,Rs)-isomers was obtained from the substrate with the opposite (R)-configuration.

Synthesis of (Rc,Ss)-1,1,1-Trifluoro-3-(p-tolylsulfinyl)-2-propanol by an Asymmetric Reduction with a Yeast, Yamadazyma farinosa, as a Key-step

Abstract (Rc,Ss)-1,1,1-trifluoro-3-(p-tolylsulfinyl)-2-propanol (>99% e.e.), an important reagent for the asymmetric protonation of substituted enolates, was prepared (70%) from (S)-methyl p-tolyl sulfoxide. The stereoselectivity of the Yamdazyma farinosa-catalyzed reduction of carbonyl groups, the key step for the introduction of an asymmetric carbon, was greatly affected by the stereochemistry of the asymmetric sulfur atom. The reduction of (S)-1,1,1-trifluoro-3-(p-tolylsulfinyl)-2-propanone proceeded smoothly and in a quite stereoselective manner to give the desired compound, while a 76 : 24 mixture of (Rc,Rs)- and (Sc,Rs)-isomers was obtained from the substrate with the opposite (R)-configuration.

Non-selectivity in the reaction of levoglucosenone with the sulfinyl allyl carbanion

Condensation of levoglucosenone with the carbanion ofrac-allyl phenyl sulfoxide, in contrast with reactions of this anion with the majority of other unsaturated ketones, proceeds without regio- or enantioselectivity to give a (1.0–1.8): 1 mixture of products of both 1,2- and 1,4-γ-addition of the allylic residue. Each product is a (1.2–1.6): 1 mixture of epimers at the asymmetric sulfur atom.

Synthesis of Ferroelectric Liquid Crystalline Polysiloxanes Having a Chiral n-Alkyl Tolansulfinate as the Pendant Group

The synthesis and mesomorphic properties of a series of ferroelectric liquid crystalline polysiloxanes bearing chiral 4-[(4-((n-alkyloxy)sulfinyl)phenyl)ethynyl]phenyl 4-(undecyloxy)benzoate as mesogenic pendant groups are presented. In these polymers, the chirality is introduced via an asymmetric sulfur atom. The synthesis of the materials was possible through three successive polymer-analogous reactions. The last key synthetic step is the polyesterification of the poly((undecyloxy)benzoic acid-methylsiloxane) with the n-alkyl 4-[(4-hydroxyphenyl)ethynyl]benzenesulfinate derivatives, which could be carried out efficiently. Up to 97% overall substitution rates of the siloxane units by the mesogenic moiety could thus be obtained. In this paper are also reported the results of the preliminary investigations of the ferroelectric properties, carried out in the S c * phase of one polymer. Finally, the comparison of the mesomorphic properties of a sulfinate-based polymer and molecule with their carboxylate-based counterparts is briefly reviewed.

Characterization of trans(O)-N,N′-Ethylenebis(S-methyl-l-cysteinato)cobalt(III) Perchlorate and the Absolute Configuration of the Complex Determined by X-Ray Analysis

Abstract A cobalt(III) complex with the sexidentate ligand, N,N′-ethylenebis(S-methyl-l-cysteine), was newly synthesized and chromatographically isolated. Of two possible geometrical isomers, trans(O) and trans(N), one isomer was formed selectively. The dark-red crystals are orthorhombic, space group P212121, a=9.055(2), b=22.123(7), c=17.111(4) Å, and Z=8. The structure was solved by the direct method and refined to R=0.066 for 2380 nonzero reflections. The complex is trans(O) isomer and the crystal consists of two kinds of complex cations with respect to the absolute configurations of the coordinated asymmetric sulfur atom. One takes an S(S),S(S) configuration and the other an R(S),S(S) one. The changes in configuration between the asymmetric sulfur atoms in the crystal and those in aqueous solution are discussed on the basis of NMR (13C and 1H) spectral studies.

STRUCTURE AND ABSOLUTE CONFIGURATION OF TRANS(O)-N,N′-ETHYLENEBIS-(S-METHYL-l-CYSTEINATO)COBALT(III) PERCHLORATE

Abstract The crystal structure of trans(O)-N,N′-ethylenebis(S-methyl-l-cysteinato)cobalt(III) perchlorate was determined by X-ray diffraction study. The structure consists of two kinds of complex cations with asymmetric sulfur atoms of different absolute configuration (S(S)S(S) and R(S)S(S)). The differences between the configurations of the sulfur atoms in crystal and those in solution are discussed.

Reduction of methionine sulfoxides by Escherichia coli

The reduction of the sulfoxides of methionine by Escherichia coli occurs in the presence of molecular hydrogen. By comparing the rates of reduction of some of the isomers of methionine sulfoxide it has been observed that the configuration of the asymmetric sulfur atom markedly influences this rate, whereas that of the α-carbon atom is of less significance. Under the same conditions, E. coli does not reduce l-cystine, cysteic acid, methionine sulfone, sulfanilamide, or marfanil. No evidence of racemization of the asymmetric sulfur atom by the organism was found.