Efficient Synthesis of Epoxides from Vicinal Diols Via Cyclic Sulfates

Reaction of cyclic sulfates of vic-diols with sodium hydroxide in THF-MeOH produced the corresponding epoxides in excellent isolated yields at room temperature. Cyclic sulfates of trans-diols gave cis-epoxides, and cyclic sulfates of cis-diols afforded trans-epoxides exclusively. Various cyclic sulfates of vic-diols can be converted into the epoxides under the conditions.     

A Convenient Method for the Synthesis of Alkenes from Vic-diols via Cyclic Sulfates with Magnesium Iodide

Reaction of cyclic sulfates of vic-diols with magnesium iodide in acetonitrile produced the corresponding olefins in excellent isolated yields at room temperature. Cyclic sulfates of trans-diols gave trans-alkenes exclusively. Cyclic sulfates of cis-diols gave a mixture of cis- and trans- alkenes. However, the cyclic sulfate of cyclic cis-diol afforded the corresponding cis-alkene only.     

Epoxide formation by the photolysis of cyclic oxalate esters

The cyclic oxalate esters from $\text{meso}$- and $\text{d}$, $\text{1}$-hydrobenzoin were prepared and photolyzed. $\text{Meso}$-hydrobenzoin oxalate gave only $\text{cis}$-stilbene oxide upon photolysis while the $\text{d}$, $\text{1}$ isomer gave $\text{trans}$-stilbene oxide.     

Electron-bombardment and pyrolysis of meso- and dl-hydrobenzoin cyclic sulfites

Only a minor yield of sulfur dioxide positive ions is eliminated from the meso- and dl-hydrobenzoin cyclic sulfite molecules under electron bombardment. Among the principal fragmentation products for both sulfites are very similar yields of ions with m/e 154 and 126, which contain sulfur most probably attached to a phenyl ring. Positive ions apparently corresponding to those of diphenylacetaldehyde, desoxybenzoin, and stilbene are minor products of the positive-ion fragmentation process of the sulfites. These three compounds along with sulfur dioxide are the products of the pyrolysis of the sulfites at 240-250°. The principal product from the meso-sulfite is desoxybenzoin, and from the dl-sulfite it is diphenylacetaldehyde. Mechanistic details are discussed.     

Reaction of Cyclic Sulfates with Phosphines

In their reactions with phosphines, cyclic sulfates 9, 10, 11, and 12 afforded corresponding olefins by way of phosphonium sulfate salts whereas sugar cyclic sulfates 21 and 22 gave anhydrosugar 23.     

A study on the stereoselectivity of C,O bond formation in esterification of cyclic thiohydroxamic acids

Esterification of cyclic thiohydroxamic acids, for example, N-hydroxypyridine-2(1H)-thione, N-hydroxy-4-methylthiazole-2(3H)-thione, and N-hydroxy-4-(p-chlorophenyl)-thiazole-2(3H)-thione, occurred with inversion of configuration at the attacked stereocenter, as evident from the use of chiral alcohols, alkyl p-toluene sulfonates, and cyclic sulfates. Stereochemical analysis of enantiomerically pure O-alkyl thiohydroxamates was performed on the basis of CD-spectroscopy and chemical derivatization. The assignment of the relative configuration in cyclic O-esters was feasible via NMR spectroscopy, whereas chiral aliphatic glycolato monoesters required hydroxyl group derivatization with chloro-(4R,5R)-bis[(1R,2S,5R)-menth-1-yloxycarbonyl)]-1,3,2-dioxaphospholane for this purpose.     

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.     

Synthesis of (-)-2s,3s, 11s,12r-2,3,11,12-tetraphenyl[18]crown-6

The synthesis of ( - ) 2S,3S,11S,12R-2, 3,11,12-tetraphenyl [18]-crown-6 from (-)-1S,2S-hydrobenzoin and meso-hydrobenzoin is described. Chemical shifts and vicinal coupling constants of the benzylic protons in the 2 S, 3 S and 11 S,12 R substructures in the free ligands and in complexes with KSCN and 1-phenylethylammonium bromides and a brief discussion of the related conformational changes are also presented. A detailed procedure for the resolution of racemic hydrobenzoin is given.     

Aluminium Mediated Glycosaminoglycan/Amyloid-β Association Mechanism

In Alzheimer’s disease, it has been proposed that glycosaminoglycans facilitate amyloid fibril formation and/or stabilize the plaque aggregates. Chondroitin sulfates are sulfated glycosaminoglycans represented an ideal distribution of charge for amyloid-β (Aβ) interactions. Recent studies have suggested a possible link between the neurotoxicity of aluminum and the pathogenesis of Alzheimer’s disease. In this paper, the interaction of Aβ with chondroitin sulfates immobilized on a chromatographic column and the role of aluminum had been studied using a biochromatographic approach (molecular chromatography). A novel biochromatographic column was developed in our laboratory for studying this interaction. This study demonstrated that the aluminum interacted with Aβ and played a role in the Aβ/chondroitin sulfates association. For a Al³⁺ concentration (x) in the medium less than 30 μmM, the Aβ/chondroitin sulfates binding decreased with x due to a decrease of the charge–charge interactions between Aβ and its chondroitin sulfates binding site. Above 30 μmM of Al³⁺ in the medium, the affinity of Aβ to chondroitin sulfates increased slightly with x because the net number of ions (n) (Al³⁺ or Cl⁻) released or bound upon complex formation is low. As well, it was clearly demonstrated, that above 30 μmM the n value depend on the Al³⁺ concentration in the bulk solvent. This dependence was due to a gradual and conformational change of the Aβ which around 80 μmM adopted a less flexible structure; its binding site was thus less accessible to Aβ and Aβ/chondroitin sulfates association decreased slightly.

     

A short and efficient synthesis of (R)-(−)-sporochnol A

A short and efficient synthesis of (R)-(−)-sporochnol A in five steps and 9% overall yield has been developed. The sequence uses as starting material the easily available enantiopure monoketal derived from 1,4-cyclohexanedione and (R,R)-hydrobenzoin that serves as a chiral auxiliary.     

Synthesis of (S)-(−)-β-cuparenone and (S)-(−)-cuparene

A short and efficient synthesis of the title compounds is described. (S)-(−)-β-Cuparenone was prepared in 31% yield from p-tolualdehyde and mesityl oxide in eight steps. Absolute stereochemistry was established by means of a diastereoselective cyclopropanation using (R,R)-hydrobenzoin as a recoverable auxiliary.     

Syntheses of chiral hybrid O,N-donor ligands for the investigation of lanthanide complex reactivities in direct aldol condensations

A method for the synthesis of new chiral α/β-dimethylamino esters and β-amino ethers from (S,S)-hydrobenzoin is described. These new O,N-donor ligands are expected to prove a useful platform for exploring the relationship between the ligand structure and stereoselective direct aldol condensation catalyzed by their lanthanide complexes. The initial survey of the catalytic utility of newly synthesized complexes in the unique aldol-Tishchenko reaction of aldehydes and aliphatic ketones is also presented.     

Synthesis of novel chiral hydrobenzoin mono-tert-butyl ethers derived from m-hydrobenzoin and their application as chiral auxiliaries in the diastereoselective reduction of α-keto esters

Three m-hydrobenzoin derived chiral hydrobenzoin mono-tert-butyl ethers were synthesized by a new reaction pathway and tested as chiral auxiliaries in the L-selectride^® mediated stereoselective reduction of their corresponding phenyl glyoxylates. As a result, improved stereoselectivities of up to a ratio of 92:8 compared to 84:16 with the initially examined analogous benzyl ether were achieved.     

An abnormal C-H?O bond directs intermolecular bonding arrangements in bisimines

N,N-bis(3-nitrobenzylidene)ethylenediamine (1) formed a supramolecule with meso-hydrobenzoin, whereas N,N-bis(4-nitrobenzylidene)ethylenediamine (2) underwent a self-assembling process. The X-ray diffraction analysis showed that C-H?O intermolecular contacts play an important role in the building of both structures.     

Spiro-sulfamidate and sulfate nucleosides via 2′ and 3′-C-branched-chain sugars and nucleosides

C-branched-chain sugars and nucleosides were obtained by organocatalysis from ulose derivatives. After a reduction step, the corresponding 1,3-diol was derivatized into 3′-spiro-sulfamidates and unexpected sulfates by treatment with a Burgess reagent. Deprotection of the Boc-derivatives was carried out while preserving the cyclic sulfate. An example of ring opening of the cyclic sulfate derivative with sodium azide leading to the corresponding 3′-C-azidoalkyl branched-chain nucleosides is given.     

Direct formation of cyclic sulfates utilising hypervalent iodine species and sulfur trioxide adducts

PhIO reacts with SO₃·DMF at 0°C to form an active sulfating reagent; subsequent addition of alkenes results in the direct formation of cyclic sulfates in moderate to good yield (35-75%). Terminal, 1,1-disubstituted and cyclopentenes participate in the reaction which is technically very straightforward to carry out.     

Chiral linker. Part 2: Synthesis and evaluation of a novel,reusable solid-supported open chain chiral auxiliary derived from m-hydrobenzoin for the diastereoselective reduction of α-keto esters

Three novel m-hydrobenzoin derived chiral hydrobenzoin mono-alkyl ethers were synthesized and evaluated as open chain chiral auxiliaries in the L-selectride^R/ZnCl₂ mediated stereoselective reduction of their corresponding phenyl glyoxylates, resulting in des of up to 91%. The optimized auxiliary structure was immobilized on commercially available Wang-resin by using the ether substituent as a sublinking unit and applied as a reusable solid-supported chiral auxiliary in the same type of reaction with only little loss of stereofacial selectivity.     

Desymmetrization of meso 7-aza-2,3-bis(phenylsulfonyl) bicyclo[2.2.1]hept-2-ene: a re-examination. Kinetic resolution of racemic 3-arylsulfonyl-7-aza-2-bromobicyclo[2.2.1]hepta-2,5-dienes

The inexpensive large scale preparation of N-methoxycarbonyl-7-aza-2,3-bis(phenylsulfonyl)bicyclo[2.2.1]hept-2-ene and the re-examination of its stereoselective desymmetrization are reported. Moreover, the kinetic resolution of N-protected 3-arylsulfonyl-7-aza-2-bromobicyclo[2.2.1]hepta-2,5-dienes promoted by (R,R)-hydrobenzoin is described, representing a new tool to fix the absolute stereochemistry of the 7-azabicyclo[2.2.1] skeleton.     

New approach to cyclic sulfites and sulfates through reactions of sulfur oxychlorides with glycidols

Reactions of 2,3-epoxyalcohols (glycidols) with thionyl chloride or sulfuryl chloride afford cyclic sulfites or sulfates, respectively. These reactions yield predominantly 4-chloroalkyl-1,3,2-dioxathiolane oxides. The configuration of the C(4) atom in the latter compounds exactly corresponds to that of the C(2) atom of the parent glycidol, whereas the configuration of the exocyclic atom is almost completely reversed with respect to that of the C(3) atom of the precursor. Published inIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 9, pp. 1586–1593, September, 2000.     

Selective Inversion of the Proximal or Distal Hydroxyl Groups in syn,syn-3-[N-(Alkoxycarbonyl)amino] 1,2-Diols via Cyclic Sulfates

The formation of cyclic sulfates (4) from syn,syn-3-[N-(benzyloxycarbonyl)amino] 1,2-diols provides a common intermediate to access other diastereomers via two inversion procedures. Thermolysis of the cyclic sulfates in acetonitrile normally leads to inversion of the distal hydroxyl group to form a 1,3-oxazin-2-one (6). Catalytic hydrogenation of the cyclic sulfates under basic conditions (NEt(3)) results in inversion at the proximal hydroxyl group to form a 1,3-oxazolidin-2-one (5).