Fluorine chemistry statistics: numbers of organofluorine compounds and publications associated with fluorine chemistry

Data are presented which demonstrate the considerable growth in the numbers of new organofluorine compounds produced annually, and also the numbers of papers and patents published concerned with fluorine chemistry. An overview of some information sources of relevance to fluorine chemists is also presented.     

Metal carbene N-H insertion of chiral α,α-dialkyl α-diazoketones. A novel and concise method for the stereocontrolled synthesis of fully substituted azetidines

The syntheses of all cis substituted azetidines were accomplished in few steps from l-serine in modest to high yields. The key step was based on a rhodium or copper carbenoid N-H insertion of α,α^′-dialkyl-α-diazoketones to furnish cis-2,4-dialkyl-azetidin-3-ones as the only observable diastereoisomers.     

Bromodifluoromethylation of aromatic Grignard reagents with CF2Br2

The bromodifluoromethylation of aromatic Grignard reagents having electron-withdrawing groups with dibromodifluoromethane (CF₂Br₂) was developed. The reaction proceeded to give the corresponding (bromodifluoromethyl)benzene derivatives via a difluorocarbene-mediated mechanism.     

Synthesis of oxygen-containing heterocyclic compounds based on the intramolecular O-H insertion and Wolff rearrangement of α-diazocarbonyl compounds

The addition products of Ti(IV)-enolate derived from β-keto α-diazo carbonyl compound to ketones or α,β-unsaturated compounds were subjected to Rh₂(OAc)₄-catalyzed and photo-induced diazo decomposition. The Rh₂(OAc)₄-catalyzed reaction afforded intramolecular O-H insertion products, while the photo-induced reaction gave Wolff rearrangement/intramolecular nucleophilic addition products. The transformations represent new approaches to tetrahydrofuran and γ-butyrolactone derivatives.     

Selective determination of organofluorine compounds by capillary column gas chromatography with an atmospheric pressure helium microwave-induced plasma detector

Fluorinated analogs of compounds typical of those found in metabolic and other biological studies are detected with high selectivity using a gas chromatograph/microwave-induced plasma detector (GC-MIPD), which permits fluorine-selective detection by monitoring the emission at 685.6 nm. Using the described atmospheric pressure helium-sustained plasma detector, the minimum detectable level, fluorine selectivity (relative to carbon), and linear dynamic range of this GC-MIPD system were determined to be 4.8 pg-F/s, 1060, and 5000, respectively. The utility of this GC-MIPD system for the selective detection of organofluorine compounds is demonstrated by its application in the analysis of the metabolic fate of a fluorinated substrate administered to a mixture of wheat germ phosphatase and potato apyrase, as well as by analysis of synthetic mixtures.     

钨卡宾络合物在有机合成中的应用

对钨卡宾络合物参与的反应机理和一些合成方法作了简要的介绍,并评述了部分钨卡宾络合物合成有机化合物的反应。     

Trapping the elusive aza-oxyallylic cation: new opportunities in heterocycloaddition chemistry

The aza-oxyallylic cation is a reactive intermediate that undergoes a [4+3] cycloaddition with dienes to form seven-membered heterocycles. Although this type of intermediate was proposed over 50 years ago, only recently has experimental evidence been obtained to support its existence. This review highlights the historical studies of aza-oxyallylic cations and their recent development as intermediates for the synthesis of heterocycles and polyheterocyclic scaffolds.     

Titanium carbene complexes as useful tools in organic synthesis

Various titanium carbene complexes are prepared by the reductive titanation of thioacetals, gem-dihalides, and related organosulfur and organohalogen compounds with the titanocene(II) reagent Cp(2)Ti[P(OEt)(3)](2). Alkylidene-, heteroatom-substituted methylidene-, 2-alkenylidene-, 2-alkynylidene-, and vinylidene-titanocenes thus formed are highly reactive toward organic compounds bearing a multiple bond and are employed for a variety of organic transformations such as carbonyl olefination and olefin metathesis.     

咪唑类氮杂环卡宾金属配合物的合成与应用研究进展

氮杂环卡宾具有独特的结构和性质,可合成大量的氮杂环卡宾金属化合物,现在已发展为催化领域的重要配体之一,一直受到大量研究者的关注。本文综述了以咪唑作为基本单元搭载不同的杂原子基团合成一系列具有单齿、双齿和多齿型金属螯合物的方法及其在Suzuki偶联、Heck偶联等反应中的应用。     

Copper-catalyzed synthesis of 3-allyl-2-aminoindoles from 3-diazoindolin-2-imines and allyltrimethylsilane

A novel and facile approach to 3-allyl-2-aminoindoles via the copper-catalyzed reaction of 3-diazoindolin-2-imines with allyltrimethylsilane is described. The domino reaction proceeds efficiently in one-pot and shows broad substrate scope with respect to the diazo substrates. Furthermore, the synthesized 3-allyl-2-aminoindoles can be conveniently transformed into 3-allyl-3-hydroxylindolin-2-imines and 3-allyl-3-fluoroindolin-2-imines.     

Template synthesis of benzannulated N-heterocyclic carbene ligands

The reaction of 2-azidophenyl isocyanide (7) with [M(CO)(5)(thf)] (M=Cr, W) yields the isocyanide complexes [M(CO)(5)(7)] (M=Cr 8, M=W 9). Complexes 8 and 9 react with tertiary phosphines such as triphenylphosphane at the azido function of the isocyanide ligand to give the 2-triphenylphosphiniminophenyl isocyanide complexes 10 (M=Cr) and 11 (M=W). The polar triphenylphosphiniminophenyl function in complexes 10 and 11 can be hydrolyzed with H(2)O/HBr to afford triphenylphosphane oxide and the complexes containing the unstable 2-aminophenyl isocyanide ligand. This ligand spontaneously cyclizes by intramolecular nucleophilic attack of the primary amine at the isocyanide carbon atom to yield the 2,3-dihydro-1H-benzimidazol-2-ylidene complexes 12 (M=Cr) and 13 (M=W). Double deprotonation of the cyclic NH,NH-carbene ligands in 12 and 13 with KOtBu and reaction with two equivalents of allyl bromide yields the N,N'-dialkylated benzannulated N-heterocyclic carbene complexes 14 (M=Cr) and 15 (M=W). The molecular structures of complexes 9 and 11-15 were confirmed by X-ray diffraction studies.     

Transition metal carbene chemistry: Nucleophilic substitution reactions of imidazolide and benzimidazolide ions with Fischer carbene complexes in MeOH

Rate constants for the nucleophilic substitution reactions of imidazolide (IZ⁻) and benzimidazolide (BIZ⁻) ions with 4-Cr-Z and 5 in MeOH at 25 °C are reported and Hammett ρ values are evaluated to be 1.50 ± 0.10 and 1.51 ± 0.08 for 4-Cr-Z-IZ⁻ and 4-Cr-Z-BIZ⁻ reactions, respectively. The comparable reactivity and also almost identical ρ values for these reactions indicate that there is no difference in sensitivity towards electronic effects due to slightly bigger size of BIZ⁻ over IZ⁻ and bond formation at the transition states are equally progressed. The higher ρ values for these reactions compared to those with a wide range of nucleophiles may arise mainly due to lower polarity of the solvent MeOH which enhances the requirement for stabilization of the negative charge in the transition state by the Z-substituents.     

Synthesis of monodentate bis(N-heterocyclic carbene) complexes of iridium: Mixed complexes of abnormal NHCs, normal NHCs, and triazole NHCs

A stepwise synthesis of mixed monodentate bis-NHC complexes of Ir(I), employing Ag(I)NHC complexes as transfer agents, yields complexes with two monodentate NHCs having different steric and electronic characteristics. The crystal structure of the mixed complex (5) with both a triazole-derived NHC ligand and an imidazole-derived NHC ligand is reported and both the NHC ring geometry and the M-NHC bond lengths are similar to related complexes. The complexes maintain their integrity over time and do not disproportionate, consistent with the NHC ligands not being labile.     

Rhodium-catalyzed NH-indole-directed ortho CH coupling of 2-arylindoles with diazo compounds via metal carbene migratory insertion

A high regioselective rhodium-catalyzed ortho CH coupling of 2-arylindoles with diazo compounds via NH-indole-directed CH bond activation has been developed. The catalytic reaction features mild reaction conditions, broad substrate scope and good functional group tolerability.     

Synthesis of nitrogen-containing compounds using chromium Fischer carbene complexes

Synthetic utility of the Fischer-type carbene complexes of chromium for the preparation of nitrogen-containing compounds is demonstrated. Alkoxy carbene complexes reacted with imines to give (optically active) 3-pyrrolines and beta-methoxy allylic amine derivatives in good yields. The amino carbene complexes reacted with alpha,beta-unsaturated aldehydes to give substituted pyrroles in good yields.     

Cu(I)-catalyzed reaction of diazo compounds with terminal alkynes: a direct synthesis of trisubstituted furans

A method for the synthesis of tri-substituted furans has been developed based on Cu(I)-catalyzed reaction of terminal alkynes with β-keto α-diazoesters. This method for the synthesis of 2,3,5-trisubstituted furans is operationally simple and applicable to wide substrate scope. Moreover, this synthesis employs cheap Cu(MeCN)₄PF₆ as the catalyst and no additional ligand is needed. Similar reaction has also been applied to ethyl (E)-2-diazo-3-(methoxyimino)butanoate for the synthesis of 2,3,5-trisubstituted N-methoxypyrroles with limited success.     

A facile synthesis of unsymmetrical ureas

A facile and versatile method for the synthesis of unsymmetrical ureas from readily available reagents is reported. In the first step trifluoroethylchloroformate is reacted with a stoichiometric amount of a primary amine to give an intermediate trifluoroethyl carbamate. The addition of a second amine (primary or secondary) to the trifluoroethyl carbamate furnishes corresponding unsymmetrical ureas in 75-85% yield. A simple workup procedure, the high yields obtained, and the purity of the isolated products are suitable for the parallel synthesis of combinatorial libraries of unsymmetrical ureas with high structural and functional diversity.     

Palladium-catalyzed cyclopropanation of electron-deficient olefins with aryldiazocarbonyl compounds

A concise and efficient protocol for the preparation of cyclopropanes from various aryldiazocarbonyl compounds and electron-deficient olefins catalyzed by Pd(OAc)₂ is reported.