A novel and efficient 4-oxothiazolidine-1,2-dithiole rearrangement induced by Lawesson's reagent

Functionalized 1,2-dithioles have been synthesized by a ring opening-closing process of 5-substituted- and 5-unsubstituted-2-alkylidene-4-oxothiazolidines with Lawesson's reagent. The ¹³C NMR data confirmed the meso-ionic structure of these aromatic-type 1,2-dithioles.     

Ultramicro Analysis of Reducing and Non-Reducing Sugars by Liquid Chromatography

Abstract

A post-column detection system for ultramicro amount of sugars has been developed using taurocyamine as the labelling reagent. Less than 10 pmol of reducing sugars were determined by this HPLC system. Non-reducing sugars were detected by the addition of periodate to the reagent.

Modification of the reaction reagent components made this detection system feasible to apply to various methods for separation of carbohydrates using pure water, acetonitrile/water mixtures, borate buffer or aqueous sodium hydroxide as the eluent.     

Asymmetric ring opening of meso-epoxides with B-halobis(2-isocaranyl)boranes 2-dIcr2BX

Hydroboration of commercially available (+)-2-carene (96% ee) with either BH₂Cl·SMe₂ or BCl₃/Me₃SiH, provides chemically pure B-chlorobis(2-isocaranyl)borane (2-^dIcr₂BCl) whereas B-bromobis(2-isocaranyl)borane (2-^dIcr₂BBr) could only be prepared by Matteson’s BBr₃/Me₃SiH procedure in high chemical yield and purity. The enantiomeric excess achieved with 2-^dIcr₂BCl (78%), was significantly higher than those realized with the previously explored reagent, ^dIpc₂BCl (41%), especially for meso-cyclohexene oxide. The new reagent, 2-^dIcr₂BBr also showed considerable improvements in enantiomeric excesses, in the cases of meso-cyclopentene oxide (67%) and meso-cis-2,3-butene oxide (78%) than those achieved with the previously reported reagent, ^dIpc₂BBr (57% and 61%, respectively).     

1,2-Diarylethylenediamines as fluorogenic reagents for catecholamines

Twenty-eight 1,2-diarylethylenediamines were investigated in a search for highly sensitive fluorogenic reagents for catecholamines (norepinephrine, epinephrine and dopamine). They all react with epinephrine used as a model catecholamine under mild conditions (pH 6.5–6.8, 37–50°C) in the presence of potassium hexacyanoferrate (III) to produce fluorescence. Of the compounds tested, 1,2-bis(3,4-dimethoxyphenyl)ethylenediamine, 1,2-bis(4-methoxyphenyl)ethylenediamine and 1,2-bis (4-ethoxyphenyl)ethylenediamine, all in the meso-form, are the most sensitive for all the catecholamines. 1,2-Diphenylethylenediamine, 1,2-bis(4-methoxyphenyl)ethylenediamine and 1,2-bis (4-methylphenyl) ethylenediamine in the dl-form are more sensitive to dopamine than the corresponding compounds in the meso-form. Catecholamines can be determined at concentrations as low as 10–15 pmol ml^?1 by using those compounds as reagents. The reactions of other catechol compounds are reported. Other types of biologically important compounds do not interfere.     

Seven-membered ring boronates at trans-diol moieties of carbohydrates

MS and ¹H, ¹³C and ¹¹B NMR results are presented revealing the formation of cyclic seven-membered boronate structures at trans-1,2-diol moieties of carbohydrates providing new opportunities for the activation, protection and analysis of glucopyranose-based oligomers and polymers such as cellulose or starch. ‘Coordination-induced shifts’ in ¹³C NMR spectra were identified for the esterification by boronic acids of carbohydrates, which can be applied for further studies.     

Aerobic oxidative desymmetrization of meso-diols with bifunctional amidoiridium catalysts bearing chiral N-sulfonyldiamine ligands

Asymmetric aerobic oxidation of a range of meso- and prochiral diols with chiral bifunctional Ir catalysts is described. A high level of chiral discrimination ability of Cp^∗Ir complexes derived from (S,S)-1,2-diphenylethylenediamine was successfully demonstrated by desymmetrization of secondary benzylic diols such as cis-indan-1,3-diol and cis-1,4-diphenylbutane-1,4-diol, providing the corresponding (R)-hydroxyl ketones with excellent chemo- and enantioselectivities. Enantiotopic group discrimination in oxidation of symmetrical primary 1,4- and 1,5-diols gave rise to chiral lactones with moderate ees under similar aerobic conditions.     

Lipase-catalyzed desymmetrization of meso-1,2-diaryl-1,2-diaminoethanes

The synthesis and enzyme-catalyzed desymmetrization of meso-1,2-diaryl-1,2-diaminoethanes have been investigated. A family of aromatic meso-1,2-diamines, containing different substitution patterns in the aromatic ring, was first prepared and then desymmetrized enantioselectively using lipases as biocatalysts. Selective alkoxycarbonylation of one of the amino groups was achieved using allyl carbonates, isolating the corresponding allyl monocarbamates with moderate to high enantiomeric excess at 45 °C. Candida antarctica lipase types A (CAL-A) and B (CAL-B) displayed the best activities and stereopreferences, with a dramatic influence being observed depending on the diamine structure. Non substituted and para-substituted aryldiamines led to the formation of allyl carbamates with good enantiomeric excess, using CAL-A for the less hindered substrates and CAL-B for the more hindered ones. On the other hand meta- and ortho-derivatives afforded low or negligible conversions and selectivities, respectively.     

A linear Cu-Gd-Cu-Gd complex derived from the assembly reaction of [NaCuH3L] and [Gd(thd)3(H2O)2] (H3L = meso-1,2-diphenyl-1-(2-oxybenzamido)-2-(2-oxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetra-methyl-3,5-heptanedione)

A linear tetranuclear Cu^II-Gd^III-Cu^II-Gd^III complex [Cu^IIL^dpen(meso)Gd^III(thd)₂(H₂O)]₂ was synthesized from the reaction of [NaCu^IIL^dpen(meso)(DMF)] with [Gd^III(thd)₃(H₂O)₂], and the structures and magnetic properties were investigated, where H₃L^dpen(meso) = meso-1,2-diphenyl-1-(2-hydroxybenzamido)-2-(2-hydroxy-3-ethoxybenzylideneamino)ethane and Hthd = 2,2,6,6-tetramethyl-3,5-heptanedione. The Cu^II complex component [NaCu^IIL^dpen(meso)(DMF)] has a one-dimensional (1D) chain structure, in which the Na⁺ ion is coordinated by two phenoxo and an ethoxy oxygen atoms of a Cu^II complex and an amido oxygen atom of the adjacent Cu^II unit to produce the 1D structure, in which the diphenylethylenediamine moieties have the array of {(1R,2S)-Na-(1S,2R)}_1∞. The assembly reaction of the Cu^II and Gd^III components gave a linear complex with the array of Cu(1)-Gd(1)-Cu(2)-Gd(2), in which two diphenylethylenediamine moieties have the same chirality of (1R,2S)-(1R,2S) or (1S,2R)-(1S,2R). Two linear Cu(1)-Gd(1)-Cu(2)-Gd(2) units are linked by hydrogen bonds through two water molecules to give a cyclic structure with a center of symmetry. The temperature dependence of the magnetic susceptibilities and field-dependent magnetization revealed the ferromagnetic interaction between the Cu^II and Gd^III ions within the linear chain.     

Chromium-catalyzed pinacol coupling of benzaldehyde in water

The pinacol coupling of benzaldehyde (0.25 M or 1.25 M) in water was catalyzed by 5-25 mol % CrCl₂ in the presence of Zn-dust or Al-dust at 20 °C or 60 °C. In all cases at most 50% of the pinacol coupling product, 1,2-diphenyl-1,2-ethanediol, was obtained with the major product, benzyl alcohol, being formed by a competitive 2e⁻ reduction of the carbonyl. The dl- to meso-diastereoselectivity of the pinacol products ranged from 0.6:1 to nearly 1:1.     

An oxidovanadium(IV) complex having a perrhenato ligand: An efficient catalyst for aerobic oxidation reactions of benzylic and propargylic alcohols

An oxidovanadium(IV) complex having a perrhenato ligand [VO(ReO₄)(4,4′-^tBubpy)₂][0.25SO₄·0.5ReO₄] (4,4′-^tBubpy = 4,4′-di-tert-butyl-2,2′-bipyridine) efficiently catalyzes not only dehydrogenative oxidation of benzylic and propargylic mono-alcohols but also oxidative CC bond cleavage of meso-1,2-diaryl-1,2-ethanediols under atmospheric molecular oxygen, affording the corresponding carbonyl compounds in good yield.     

The use of chiral solvents to distinguish meso from d or 1 diastereoisomers

The 56·4 MHz ¹⁹F spectrum of a mixture of meso and dl 1,2-difluoro-1,2 dichloroethane in L -bornyl acetate resolved the ¹⁹F resonances of the separate d and l stereoisomers, thus identifying the dl spectrum, but not those of the meso isomer. These observations are considered with other examples of the use of chiral solvents to distinguish meso and dl isomers.     

Pd-Catalyzed asymmetric transformations involving P*-mono- and P*,N-bidentate diamidophosphites derived from (2S,3S)-N 2,3-dimethyl-N 1-phenylpentane-1,2-diamine

The synthesis of new P*-mono- and P*,N-bidentate diamidophosphites, containing 1,3,2-diazaphospholidine rings formed starting from (2S,3S)-N ²,3-dimethyl-N ¹-phenylpentane-1,2-diamine, is described. Comparison of their efficiency in the Pd-catalyzed enantioselective allylation with (E)-1,3-diphenylallyl acetate showed that up to 97% ee was reached in the reaction involving dimethyl malonate as a C-nucleophile. The Pd-catalyzed desymmetrization of N,N′-ditosyl-meso-cyclopent-4-ene-1,3-diol biscarbamate gave up to 61% ee.     

Caged phosphorane with P-C bond based on chloral and 4,5-dimethyl-2-(2-oxo-1,2-diphenylethoxy)-1,3,2-dioxaphospholane

The key methods of caged phosphoranes synthesis are analyzed. Reaction of 4,5-dimethyl-2-(2-oxo-1,2-diphenylethoxy)-1,3,2-dioxaphospholane (prepared from the meso-form of 2,3-butanediol) with chloral has yielded the caged phosphorane containing a phosphorus-carbon bond: 1,1-(1,2-dimethylethylenedioxy)-3,4-diphenyl-6-trichloromethyl-2,5,7,1-trioxaphosphabicyclo[2.2.1^1,4]heptane; spatial structure of the product has been elucidated with X-ray diffraction analysis.

     

Desymmetrization of meso-methylenecyclopropanes by a palladium-catalyzed asymmetric ring-opening bis(alkoxycarbonylation) reaction

Desymmetrization of various meso-methylenecyclopropanes was accomplished by a palladium-catalyzed asymmetric ring-opening bis(alkoxycarbonylation) reaction employing a chiral bioxazoline ligand. The reaction proceeded smoothly in the presence of copper(I) triflate under carbon monoxide and oxygen at ambient pressure to give the corresponding optically active α-methyleneglutarates with up to 60% ee. Desymmetrization of protected meso-(3-methylenecyclopropane-1,2-diyl)dimethanols was also carried out to give enantioenriched highly oxygen-functionalized α-methyleneglutarates.     

Synthesis,molecular structure and reactivity of the dimethyl sulfide adduct of a 1,3,2-diselenaborolane with an annelated dicarba-closo-dodecaborane(12) unit

The reaction of 1,2-diselenolato-1,2-dicarba-closo-dodecaborane(12) dianion [1,2-(1,2-C₂B₁₀H₁₀)Se₂]²⁻ with HBBr₂–SMe₂ affords the dimethyl sulfide adduct of 4,5-[1,2-dicarba-closo-dodecaborano(12)]-1,3-diselena-2-borolane in good yield. The molecular structure was determined by X-ray diffraction, and the solution-state structure was established by NMR spectroscopy (¹H, ¹¹B, ¹³C, ⁷⁷Se NMR). ¹¹B and ⁷⁷Se chemical shifts were reproduced by DFT calculations. Attempts were made to abstract dimethyl sulfide, and the parent donor-free compound could be detected in solution. The reactivity of the title compound was studied towards pyridine, Me₃SnF, [Pt(PPh₃)₂(C₂H₄)], tert-Bu-OH, AlMe₃ and AlH₃-N(Et)Me₂ as well as a hydroborating reagent.     

(Salen)Ti(IV) complex catalyzed asymmetric ring-opening of epoxides using dithiophosphorus acid as the nucleophile

A series of chiral bis-Schiff bases were synthesized starting from (1R,2R)-(+)-diaminocyclohexane, (+)-cis-1,2,2-trimethyl-1,3-diaminocyclopentane, (R)-2,2^′-diamino-1,1^′-binaphthalene, and (1S,2S)-diphenyl-1,2-ethanediamine. The enantioselective ring-opening of meso epoxides with dithiophosphorus acids catalyzed by a (salen)Ti(IV) complex formed in situ upon the treatment of Ti(OPr-i)₄ and the aforementioned chiral Schiff base was realized. The resulting products were obtained with low to good enantioselectivities (up to 73% ee). The (salen)Ti(IV) complex containing the backbone of 1,2-diaminocyclohexane exhibited the best enantioselectivity. The substituents in dithiophosphorus acids and those on the salen aromatic ring have a significant influence on the reaction. Moderate enantioselectivity were obtained for the (salen)Ti(IV) complex catalyzed ring-opening of racemic monosubstituted epoxides. High regioselectivity was observed for the alkyl substituted epoxides, whereas poor regioselectivity was obtained for the aryl substituted ones.     

Diastereoselective synthesis of 4,5-dihydroxyimidazolidin-2-ones (-thiones) and their structure

Studies on the synthesis of 4,5-dihydroxyimidazolidin-2-ones (-thiones) based on the condensation of ureas or thioureas with glyoxal or 1,2-dioxo-1,2-diphenylethane showed high diastereoselectivity in the formation of racemates (trans-diastereomers) of 4,5-dihydroxyimidazolidin-2-ones (-thiones) and meso-forms (cis-diastereomers) of 4,5-dihydroxy-4,5-diphenyl-1,3-dialkylimidazolidine-2-thiones; plausible mechanisms of their formation were suggested. X-ray diffraction studies confirmed structures of diastereomers for separate examples of racemates and meso-forms of 4,5-dihydroxyimidazolidin-2-ones (-thiones).     

Asymmetric oxidation of 1,2-diols using N-bromosuccinimide in the presence of chiral copper catalyst

Asymmetric oxidation of 1,2-diols using N-bromosuccinimide (NBS) in the presence of copper(II) triflate and (R,R)-Ph-BOX has been exploited. This oxidation was applicable to asymmetric desymmetrization of meso-hydrobenzoin and kinetic resolution of dl-hydrobenzoin and racemic-cycloalkane-cis-1,2-diols to afford optically active α-ketoalcohols with good to high enantiomeric excess.     

Catalytic dissymmetrization of meso-2-imidazolidinones: alternative route to chiral synthons for 1,2-diamines

The chiral functionalization of a simple heterocycle, 1,3-dihydro-2-imidazolone, was achieved by the highly enantioselective monodeacylation of meso-1,3-diacetyl-2-imidazolidinones via an oxazaborolidine-catalyzed borane reduction. This kinetically controlled dissymmetrization is sufficiently effective to provide a synthetic route to either enantiomer of (4S, 5S)- or (4R, 5R)-4,5-dimethoxy-2-imidazolidinone derivatives, which serve as chiral synthons for threo-1,2-diamines.     

Desulfation of Sulfated Carbohydrates Mediated by Silylating Reagents

Abstract

Efficient methods of desulfation are often required in carbohydrate chemistry and biochemistry. In addition to conventional desulfation methods,^1,2 we recently reported a novel desulfation method employing a silylating reagent, N,O-bis(trimethylsilyl)-acetamide.^3,4 With this reagent, the 6-O-sulfoxyl groups of the sugar moiety are regioselectively removed and newly formed hydroxyl groups are further converted by silylation into trimethylsilyloxyl groups. The desulfated carbohydrates are easily recovered after desilylation with water or aqueous methanol. Although the mechanism for this reaction remains unclear, silylating reagents can be considered as potential reagents for desulfation reaction. In the present paper, we examined various silylating reagents to find effective and new desulfation reagents for carbohydrate sulfates.