2,3-Dichlorobicyclo[2.2.1]hepta-2,5-diene: A Convenient Precursor of Norbornadiene-2,3-diynes

Norbornadienes that feature the properties of norbornadiene and of the ene-diyne in the same molecule have been prepared via a simple and high-yielding route starting fromdichlorobicyclo[2.2.1]hepta-2,5-diene (1).     

A Practical Asymmetric Synthesis of A Pseudomonic Acid Precursor from D-Arabinose or D-Xylose

The asymmetric synthesis of multi-gram quantities of a pseudomonic acid precursor is described. Improvements on the literature synthesis of diacetyl arabinal from arabinose are also reported.     

A Practical Synthesis of 1,4,7,10-Tetraaza-Cyclododecane,A Pivotal Precursor for MRI Contrast Agents

A practical preparation of the versatile macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) was developed starting from cheap and easily available starting materials as ethylenediamine and glyoxal.     

An Enzymatic Enantioselective Route to Methyl Carboxylate 2,3 - Methanohomoserine γ-Lactone; A Precursor of Chiral 2,3 - Methanohomoserine

Enzymatic hydrolysis of Dimethyl 2 - (tetrahydropyranyl) hydroxymethyl cyclopropane 1,1 - dicarboxylate 6 with an industrial esterase, followed by a deprotection of tetrahydropyranyl ether affords the title compound in 20% yield.     

beta-Glycosides of 2,3-Diazido-2,3-dideoxy-D-mannose, a Synthetic Precursor of a Rare Bacterial Cell-Wall Building Unit

2,3-Diazido-2,3-dideoxy-beta-D-mannopyranoside derivatives were synthesized in order to prepare beta-glycosides of 2,3-diacetamido-2,3-dideoxy-D-mannuronic acid, a rare moiety of bacterial oligosaccharides. A direct glycosyl donor, 4,6-di-O-acetyl-2,3-diazido-2,3-dideoxy-alpha-D-mannopyranosyl bromide, was prepared, and its synthetic capacity was tested in glycosylation reactions. An indirect route was also elaborated: 3-azido-3-deoxy-beta-D-glucopyranosides were converted into beta-D-mannopyranosides. The cis vicinal diazido function successfully tolerated the conditions of mild acidic hydrolysis, tritylation, Jones oxidation, TEMPO oxidation, acetolysis, and bromination with TiBr(4).     

A Practical Synthesis of Chiral 3-Chloro-2-hydroxyalkanoates and 2,3-Epoxyalcohols

Asymmetric reduction of 3-chloro-2-oxoalkanoates with baker's yeast gave optically active 3-chloro-2-hydroxyalkanoates with ≥95% e.e. in most cases, which were converted to optically active 2,3-epoxyalcohols with ≥78.0% e.e.     

Synthesis of L-2,3-Diaminopropionic Acid,a Siderophore and Antibiotic Precursor

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Syntheses and Characterization of Two Adducts Based on 2,3-Diaminoquinoxaline with Imidazoquinoxaline as Precursor

The reactions of imidazoquinoxaline and 1,3,5-H3 btc acid under different condition have been investigated. The different degree of hydrolysis reaction leads to two different adducts being produced, namely, [(Hdiam Quin)+(H2btc)-](1), and [(diam Quin)4(Imi Quin)·4H2O](2). Both compounds were characterized by X-ray crystallography. Crystal data for 1: monoclinic, space group Pn with a = 9.868(2), b = 5.3172(11), c = 15.387(3) ?, β = 91.10(3)o, C17H14N4O6, Mr = 370.32, V = 807.2(3) ?3, Z = 2, Dc = 1.524 g/cm~3, μ(Mo Kα) = 0.118 mm-1, F(000) = 384, the final R = 0.0385 and w R = 0.0869 for 2294 observed reflections(I 2σ(I)). Crystal data for 2: triclinic, space group P1 with a = 9.825(2), b = 14.144(3), c = 16.054(3) ?, α = 101.06(3), β = 102.55(3), γ = 92.46(3)o, C_(44)H40N_(20)O_4, Mr = 912.96, V = 2128.8(7) ?3, Z = 2, Dc = 1.424 g/cm~3, μ(Mo Kα) = 0.099 mm-1, F(000) = 952, the final R = 0.0554 and w R = 0.1662 for 6563 observed reflections(I 2σ(I)). X-ray diffraction analysis reveals that compound 1 is a salt. Imidazoquinoxaline was wholly hydrolyzed into 2,3-diaminoquinoxaline and protonated as a cation with H2btc-acting as an anion. However, in compound 2, the imidazoquinoxaline is only partly hydrolyzed, and the resulting 2,3-diaminoquinoxaline forms adduct with the intacted imidazoquinoxaline. Both are further aggregated into 3D frameworks by strong hydrogen bonding even π-π interactions.     

Practical synthesis of 2,3-dimethoxy-5-hydroxymethyl-6-methyl-1,4-benzoquinone

2,3-dimethoxy-5-hydroxymethyl-6-methyl-1,4-benzoquinone (V) was prepared with a 75 % yield by means of a reaction sequence starting from 2,3,4,5-tetramethoxytoluene via Blanc chloromethylation reaction, Kornblum oxidation, NaBH₄ reduction and ceric ammonium nitrate oxidation. The procedure is operationally simple and amenable to gram-scale synthesis.     

A Two Step Synthesis of the Nucleoside Q Precursor 2-Amino-5-cyanopyrrolo[2,3-d]pyrimidin 4-one (PreQo)

PreQ_o (1) is prepared in a 70 % yield by the condensation of chloro(formyl)acetonitrile (2) with 2,6-diaminopyrimidin-4-one (3), and subsequently converted to its amide derivative 5. Isolation of the intermediate 4 in the condensation reaction was also observed giving further insight into the proposed mechanism.     

A Method for the Synthesis of 2,3-Disubstituted 2,3-Dihydrobenzofurans

Summary.  The synthesis of 2,3-disubstituted 2,3-dihydrobenzofuran diastereomers is described. The key step in the reaction sequence is the chemoselective reduction of a tert. alcohole with tert.-butylamine-borane/AlCl₃. The relative configuration of the substituents on the dihydrofurane moiety was assigned via NMR spectroscopy. Received September 7, 1999. Accepted November 9, 1999     

A Stereocontrolled Synthesis of a Lincosamine Precursor.

ABSTRACT

We report the first stereocontrolled synthesis of the protected lincosamine 2d, the sugar moiety of the clinically important antibiotic lyncomycine.¹ To achieve the synthesis of 1, the key structural problem to be solved is the formation of the chiral center C-6 in the D-glycero configuration. In the numerous previous attempts made from D-galactose,² very little success was obtained as far as stereocontrol is concerned. A fully synthetic route to (±)-methyl-β-lincosaminide was also reported.³     

A practical synthesis of 2,3-dihydro-2-benzofurancarboxylic acid: A general route to 2,3-dihydrobenzofurans

A practical synthesis of 2,3-dihydro-2-benzofurancarboxylic acid is reported in five steps and approximately 40% overall yield. The methodology offers a useful new route to 2-substituted-2,3-dihydrobenzofurans.     

A novel synthesis of 2,3-diaminophenazine

The title heterocyclic 2,3-diaminophenazine (DAP) hydrochloride with the crystallization solvent were obtained from three different routes and their structures were determined by X-ray diffraction, elemental analysis, and IR.