Stereoselective synthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-ulose via autoxidation reaction

Many different approaches for synthesis of branched chain sugars have beenestablished,1 because they are very useful intermediates for synthesis of other non-sugar chiralmolecules, and usually occur in nature. Branched chain glycosidulose can be used for construction offive- and six-membered carbocyclic rings to which two chiral carbons of sugar are incorporated byintramolecular aldol condensation and Robinson annulation,2 Therefore they are useful in thesynthesis of natural products which consist of annulated carbohydrates or where a highlyfunctionalised enantiomerically pure cyclopentane or cyclohexane is required. Also, this type ofbranched chain sugar can be considered as the synthons of monoterpenoid natural products of theiridoid class which have the cyclopentan-(c)-pyran structure. In view of the importance of branchedchain glycosiduloses, it is desirable to have a general, convenient methodology to their synthesis.However, none of the literature methods was reported on their synthesis by a nuclephilic addition toa partially protected glycosidulose, due to the fact that these glycosiduloses are very difficult tosynthesize selectively and unstable;3 and what is more, one-step synthesis branched chainglycosidulose using this method is almost impossible.In this paper, we report on a general, convenient method for stereoselective syntheses of2,2-bis(C-branched-chain)glucopyranosid-3-uloses by the new reaction of 1 with various activemethylene compounds. The generality of this method was examined in detail. The optimumtemperature was 18-25℃. The solvent DMF was better than the others. In all cases he yields werehigher than 60%.All the 2,2-bis(C-branched-chain)glucopyranosid-3-uloses were characterized by X-raycrystallographic analyses. In addition, the important iintermediate in this reaction was isolated,which is the product of autoxidation of 1 at C-3 position. Thus the reaction mechanism for thesynthesis of 2,2-bis(C-branched-chain) glucopyranosid-3-uloses can be rationalized by autoxidationof 1 followed by 1,4-Michael addition of various carbanions as the main steps.     

A New Approach to the Synthesis of 2-Nitrobenzaldehyde. Reactivity and Molecular Structure Studies

Summary.  New approaches to the synthesis of 2-nitrobenzaldehyde by formation and selective isomer separation of 2-nitrophenyl-1,3-dioxolane and further hydrolysis are reported. In this route, the same acidic heterogeneous catalyst is used for 1,3-dioxolane formation and hydrolysis; it can be recycled several times without loss of efficiency. The ortho/meta isomers of 2-nitrophenyl-1,3-dioxolane can be separated by a combination of stereoselective crystallization and fractionated distillation. This new route reduces safety and environmental hazards in the synthesis of 2-nitro- and 3-nitro-benzaldehydes. The molecular structures of the nitro derivatives were confirmed by ¹H and ¹³C NMR spectroscopy. The results are in accordance with a non-coplanar conformer of the 2-nitro derivatives (2-nitrobenzaldehyde and 2-(2′-nitrophenyl)-1,3-dioxolane), where the nitro group is twisted with respect to the phenyl ring. In contrary, both the carbonyl and the nitro group are coplanar with the phenyl ring in 3-nitrobenzaldehyde. This result is consistent with the reactivity of the compounds. Received January 22, 2001. Accepted (revised) July 18, 2001     

Polarographic behaviour of 2-benzilidenimino-benzohydroxamic acid (2-BIBH) and 2-BIBH-Mo(VI) system

The polarographic behaviour of 2-benzilideniminobenzohydroxamic acid (2-BIBH) solutions and of 2-BIBH solutions in the presence of Mo(VI) have been studied by using differential pulse polarography and cyclic voltammetry. The polarographic characteristics of the resulting waves have been studied and possible mechanisms of the processes involved have been proposed. A linear relationship has been observed betweenI _p and Mo(VI) concentration in the range 2×10^–6 to 1.6×10^–5 M when using 3×10^–4 M 2-BIBH. Standard deviations of 5.6×10^–8 and 1.2×10^–8 M were found for 3×10^–6 and 8 × 10^–6 M Mo(VI), respectively.     

Efficient Synthesis of Functionalized 2H-Thiopyrans via Hetero-Diels-Alder Reactions of an Enaminothione with Electrophilic Olefins

Summary.  The hetero-Diels-Alder reaction of 3-dimethylamino-1-(2-thienyl)-2-propene-1-thione (diene) with substituted β-nitrostyrenes, as well as maleic and fumaric acids (dienophiles) yielded 3,4-dihydro-2H-thiopyran derivatives. The treatment of some of those cycloadducts with acetic acid caused elimination of dimethylamine, affording stable 2H-thiopyrans. A reaction of the diene with maleic anhydride furnished a cycloadduct which underwent spontaneous rearrangement to form an N,N-dimethylamide derivative. Cycloadditions of the diene to maleimide, N-phenylmaleimide, maleic acid monoanilide, diethyl maleate, fumarate, and butenolide carried out in the presence of acetic anhydride were followed by elimination of dimethylamine under formation of stable 2H-thiopyran derivatives. Received February 19, 2001. Accepted (revised) March 12, 2001     

Synthesis and Structure of O-silylated 2-Polyfluoroacyl-cycloalkanones

Summary.  2-Acyl-cycloalkanones containing polyfluoroalkyl groups react with dichlorodimethylsilane to form the corresponding heterocyclic bis-enol derivatives. The reaction of 2-polyfluoroacyl-cycloalkanones with chlorotrimethylsilane leads to mixtures of the corresponding (Z)-configured O-silylethers. The silatropy process in this case is slow on the NMR time scale. Received February 26, 2001. Accepted (revised) March 27, 2001     

A Short and Efficient Synthesis of Novel N-(2,3-dihydro-2-oxo-5-phenyl-1H-1,4-benzodiazepin-3-yl)-2-carboxamides

Summary.  Several novel N-(2,3-dihydro-2-oxo-5-phenyl-1H-1,4-benzodiazepin-3-yl)-2-carboxamides were prepared by acyl coupling of 2-aminobenzophenones with α-(benzotriazol-1-yl)-N-acylglycines followed by displacement of the benzotriazole ring with ammonia and cyclization of the resulting monoacyl aminals. In addition to high yields and shorter reaction sequences due to avoiding deprotection and acylation of the protected 3-amino-1,4-benzodiazepin-2-one intermediates, the present approach did not involve the use of toxic and odoriferous materials as is the case with other methods. Received September 20, 2000. Accepted (revised) November 29, 2000     

Synthesis of Novel 2-Aminothiophene-3-carboxylates by Variations of the Gewald Reaction

Summary.  The synthesis of the title compounds through variations of the Gewald reaction is presented. Knoevenagel condensation of methylketone derivatives with methyl cyanoacetate and subsequent treatment of the α,β-unsaturated nitriles with sulfur and amine resulted in the corresponding 2-aminothiophenes 5 or isomers 9 and 10. Reaction of methylketone derivatives bearing a leaving group at the methyl group under modified Gewald conditions selectively led to the formation of 4-substituted 2-aminothiophenes 9a and 12. The introduction of the sulfur atom occurs through nucleophilic displacement with sodium sulfide. Received July 5, 2000. Accepted (revised) August 23, 2000     

Speciation of Cr(III) and Cr(VI) by Means of Melamine-Urea-Formaldehyde Resin and FAAS

 A method is described for the quantitative preconcentration and separation of trace chromium in water by adsorption on melamine-urea-formaldehyde resin. Cr(VI) is enriched from aqueous solutions on the resin. After elution the Cr(VI) is determined by FAAS. The capacity of the resin is maximal at ∼ pH 2. Total chromium can be determined by the method after oxidation of Cr(III) to Cr(VI) by hydrogen peroxide. The relative standard deviations (10 replicate analyses) for 10 mg/L levels of Cr(VI), Cr(III) and total chromium were 1.5, 3.5 and 2.8% respectively. The procedure has been applied to the determination and speciation of chromium in lake water, tap water and chromium-plating baths.     

Enantioselective Catalysis CXLI [1]. Tridentate Ligands with 1-(Pyridin-2-yl)ethylamine as Chiral Building Block in the Enantioselective Transfer Hydrogenation of Acetophenone

Summary.  A series of novel tridentate ligands with nitrogen and oxygen donor sites was synthesized starting from enantiomerically pure (S)- and (R)-1-(pyridin-2-yl)ethylamine, the preparation and resolution of which was developed. The new optically active ligands were tested as in situ catalysts together with Ru(PPh₃)₃Cl₂ in the enantioselective transfer hydrogenation of acetophenone with isopropanol. The secondary amine ligand (S)-2,4-di-tert-butyl-6-(1-(pyridin-2-yl)ethylamino)methylphenol gave the best results with almost quantitative conversion and 47%ee. Received August 17, 2001. Accepted August 27, 2001     

Synthesis, Characterization, and Biological Activity of n-Tributyltin Derivatives of Pharmaceutically Active Carboxylates

Summary.  Tributyltin(IV) derivatives of six different pharmaceutically active carboxylates were synthesized. The complexes were characterized by different analytical techniques (elemental analysis; infrared, NMR, and mass spectroscopy). ¹¹⁹Sn NMR data were also recorded in six different coordinating and non-coordinating solvents. The antibacterial activities of the compounds were tested using ten different bacteria relative to the reference drugs ampicillin and cephalexin. Received September 20, 2001. Accepted (revised) December 6, 2001     

Monophthalates with Oxidized C5-Carbon in the Ester Chain: A Simple Synthetic Access to Two Major Metabolites of Bis-(2-ethylhexyl)-phthalate

Summary.  The synthesis of two oxidized metabolites of bis-(2-ethylhexyl)-phthalate is described. The target structures were obtained by esterification of the appropriate alcohol carrying a protected hydroxy group with phthalic anhydride, followed by deprotection and further oxidation. Received February 26, 2002. Accepted March 6, 2002     

Kinetics of the Formation of the Blue Complex CrO(O2)2 Formed by Dichromate and H2O2 in Acid Solutions. A Stopped-Flow Investigation Using Rapid-Scan UV-VIS Detection

Summary.  The kinetics of the CrO(O₂)₂ formation by H₂O₂ and Cr₂O₇ ²⁻ in aqueous acidic media was measured at 293 ± 2 K in a pH range between 2.5 and 3.3. Using the stopped-flow method with rapid scan UV-VIS detection, the rate law of the formation of CrO(O₂)₂ was determined. For the media HClO₄, HNO₃ and CH₃COOH, the reaction order in the Cr₂O₇ ²⁻ concentration was found to be 0.5. For [H₂O₂] as well as for [H⁺], the reaction was first order in all acids used. In HCl and H₂SO₄ media the reaction was first order in Cr₂O₇ ²⁻. At T = 293 ± 2 K the rate constant for the formation of Cr(O)(O₂)₂ was found to be (7.3 ± 1.9) · 10² M^−3/2 s⁻¹ in HClO₄. Corresponding author. E-mail: grampp@ptc.tu-graz.ac.at Received January 30, 2002; accepted (revised) June 5, 2002     

A New and Simple Synthesis of 3H-Benzo[f]chromen-3-one and 2H-Benzo[h]chromen-2-one Derivatives

Summary.  Protonation of the highly reactive 1:1-intermediate produced in the reaction between triphenylphosphine and dimethyl acetylenedicarboxylate by naphthols lead to vinyl triphenylphosphonium salts which undergo an aromatic electrophilic substitution reaction with the conjugated base to produce the title compounds. Received August 14, 2001. Accepted November 22, 2001     

Synthesis and Basicity of 4-Amino-2-phenylquinazolines

Summary.  A new group of 6- and 7-substituted compounds of 4-amino-2-phenylquinazoline were synthesized by reaction of N-arylbenzimidoyl chlorides with cyanamide in the presence of TiCl₄. The products were identified by spectroscopic methods, their dissociation constants were determined and are discussed. Received February 14, 2000. Accepted February 26, 2000     

Synthesis and Anti-Hepatitis B Virus Activity of Glucosylated 2-O-Ethyluracils

Summary.  2-O-Ethyluracils were silylated with HMDS and condensed in the presence of TMS-triflate with β-D-glucose pentaacetate to give the corresponding β-nucleosides. Alternatively, these could be synthesized by nucleoside coupling of 2,3,4,6-tetra-O-acetyl-α-D-glucopyranosyl bromide with the sodium salts of 2-O-ethyluracils, which were deprotected with saturated ammonia in methanol. 6′-O-Tosylate nucleoside derivatives were prepared by treating of the latter with tosyl chloride in anhydrous pyridine. The compounds thus obtained were treated with sodium azide in anhydrous DMF to afford the corresponding 6′-azido nucleoside derivatives, which can also be prepared by treatment with sodium azide in the presence of carbon tetrabromide and triphenylphosphine in anhydrous DMF. Nucleophilic displacement of the 6′-tosyloxy group by morpholine gave 6′-deoxy-6′-morpholino nucleosides. The reduction of the azido group of the 6′-azido nucleosides using triphenylphosphine in pyridine afforded the 6′-amino analogues. Glucosylated 2-O-ethyluracils showed moderate activity against HBV. E-mail: adelnassar63@hotmail.com Received September 16, 2002; accepted (revised) October 15, 2002 Published online April 24, 2003     

Polygermanosilyne Calcium Hydroxide Intercalation Compounds Formed by Topotactic Transformation of Ca(Si 1 − x Ge x )2 Alloy Zintl Phases in Ambient Atmosphere

Summary.   Epitaxial thin films of Ca(Si _1 − x Ge _x )₂ with 0 < x ≤ 1 are found to react with the moisture of ambient atmosphere to form new Ca-Si-Ge-O-H compounds which were studied by X-ray diffraction, energy dispersive X-ray analysis, infrared absorption, and thermally induced hydrogen desorption measurements. Pure CaGe₂ forms the polygermyne calcium hydroxide intercalation compound Ca(OH)₂(GeH)₂ upon exposure to humidity, with a trigonal tr6 crystal lattice with a = 4.00(1) and c = 65.3(1)?. In mixed Ca(Si _1 − x Ge _x )₂ with smaller Ge content, the group-14 layers are subject to intense oxidation leading to decreased crystallinity. The products exhibit characteristic colours and intense photoluminescence, the peak luminescence varying from 1.35 eV for the reaction product of Ca(Si_0.3Ge_0.7)₂ to 2.6 eV for that of Ca(Si_0.5Ge_0.5)₂. Received March 12, 2001. Accepted (revised) May 2, 2001     

Synthesis of 2-Acetamido-5,6-dihalophenyl Acetates

Summary.  2-Acetamido-5,6-dihalophenyl acetates were synthesized as intermediates for the preparation of 6, 7-dihalo-8-quinolinols via the Skraup procedure. Received January 24, 2000. Accepted February 12, 2000     

On the Synthesis and Reactions of Indole-2-carboxylic Acid Hydrazide

Summary.  Indole-2-carboxylic acid hydrazide was prepared and allowed to react with aromatic aldehydes in acidic medium to give the corresponding hydrazone derivatives in good yields. The hydrazones were cyclized to indolo[2,3-d]pyridazine derivatives by refluxing with acetyl chloride. The indole carbohydrazide was converted to 2-triazolylindoles which acted as starting materials for several indole derivatives. A number of new indole derivatives were also prepared and structurally confirmed. Received October 17, 2000. Accepted (revised) December 12, 2000     

Synthesis of benzofurans via Pd-catalyzed oxidative cyclization of 2-allylphenols

Substituted 2-methylbenzofurans were obtained from 2-allylphenols via Pd²⁺-catalyzed oxidative cyclization using Cu(OAc)₂–LiCl as a reoxidant and wet DMF as a solvent.     

Synthesis of 1,5-Disubstituted 3-(4-Hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-pyrazolines

Summary. A series of 1,5-disubstituted 3-(4-hydroxy-6-methyl-2-oxo-2H-pyran-3-yl)-2-pyrazolines were synthesized by the reaction of α,β-unsaturated ketones derived from dehydroacetic acid and hydrazine in hot acetic acid or propionic acid. The structures of all new compounds were elucidated by microanalyses, ¹H and ¹³C NMR, IR, and mass spectroscopic measurements.