Showing papers on "Diazomethane published in 2005"

Hygrocins a and B, naphthoquinone macrolides from Streptomyces hygroscopicus.

Abstract: Two new naphthoquinone macrolides, hygrocins A (1) and B (2), were isolated from the fermentation broth of Streptomyces hygroscopicus. Hygrocin A is not stable due to the presence of an active methylene group (C-22), which undergoes intramolecular aldol condensation with the quinone ring to yield a γ-lactam derivative, 6. Its structural elucidation was achieved by chemical conversion to 3, an unusual diazomethane derivative, and confirmed by its alkaline hydrolysis product 4, hydrogenation derivative 5, and “degradation” product 6. The structure of hygrocin B was determined by combined chemical and spectroscopic methods.

Preparation of poly(phenyl)acetylenes having diazo groups and magnetic characterization of poly(carbene).

Abstract: (2,6-Dibromo-4-ethynylphenyl)(2,6-dimethyl-4-tert-butylphenyl)diazomethane was found to be stable enough to survive under Rh-complex-catalyzed polymerization conditions and underwent polymerization to give a phenylacetylene polymer having diazo functional groups intact with an average molecular weight of 86 000 (polystyrene standard). The products from irradiation of the polymer were characterized by SQUID measurements, which revealed that a persistent triplet carbene unit incorporated into a pi-network of the phenylacetylene polymer indeed acts as a spin source to generate a high-spin ground state, although the estimated spin multiplicities are not as high as that expected from the degree of polymerization. The finding unequivocally shows that a precursor diazo unit can basically be handled as a building block to construct polydiazo compounds and that persistent triplet carbenes, even though they greatly lose typical reactivity as a triplet carbene, still retain electronic properties and act as a spin source when aligned properly in the pi-electron frameworks to generate a high-spin molecule.

Preparation of Copper Ion Complexes of Sterically Congested Diaryldiazomethanes Having a Pyridine Ligand and Characterization of Their Photoproducts

Abstract: To realize fairly stable high-spin polycarbenes by utilizing heterospin systems comprising 2p spins of organic radicals and 3d spins of magnetic metal ions, we prepared dianthryldiazomethanes having two pyridyl groups at the 2,2‘- or 2,7-positions, that is, bis[10-(4-tert-butyl-2,6-dimethylphenyl)-2-(4-pyridyl)-9-anthryl]diazomethane (2,2‘-DPy-1−N2) and [10-(4-tert-butyl-2,6-dimethylphenyl)-9-anthryl][(10-(4-tert-butyl-2,6-dimethylphenyl)-2,7-di(4-pyridyl)-9-anthryl]diazomethane (2,7-DPy-1−N2). The triplet carbene DPy-31 generated by photolysis of DPy-1−N2 was characterized by ESR and UV−vis spectroscopy in a matrix at low temperature as well as by time-resolved UV−vis in solution at room temperature. The results showed that the triplet carbene DPy-31 was destabilized to some extent as opposed to the parent triplet carbene before pyridination, but it was still fairly persistent, having a half-life of more than 30 min in solution at room temperature. Photoproducts from the complex between DPy-1−N2 and Cu(h...

Making use of crystallization-induced asymmetric transformations in solid state organic photochemistry: application to the enantioselective Yang photocyclization of endo-bicyclo[2.1.1]hexyl aryl ketones

Abstract: Achiral endo-bicyclo[2.1.1]hexyl aryl keto-acid 1a exists in solution as a rapidly equilibrating 1∶1 mixture of enantiomers. When a solution of this compound is treated with an optically pure amine, a crystallization-induced asymmetric transformation of the second kind takes place, and crystals of only one of the two possible diastereomeric salts are deposited. Irradiation of the crystals leads to a diastereoselective Yang photocyclization reaction of the carboxylate anion portion of the salt, and following diazomethane workup to form the corresponding methyl ester, high yields of novel cyclobutanols of structure 2 are formed in enantiomeric excesses as high as 90%.

Low‐Molecular‐Weight Poly(α‐methyl β,L‐malate) of Microbial Origin: Synthesis and Crystallization

Abstract: Low-molecular-weight poly(alpha-methyl beta,L-malate) made of approximately 25-30 units was prepared from microbial poly(beta,L-malic acid) by treatment with diazomethane. The thermal characterization of the polymalate methyl ester was carried out and its crystalline structure was preliminary examined. Its ability to crystallize both from solution and from the melt was comparatively evaluated.

Reactions of diazoalkanes with unsaturated compounds 15. Catalytic reactions of unsaturated carbonyl compounds and their derivatives with diazomethane

Abstract: The present study concerned with the influence of the nature of the acetal fragment in unsaturated compounds on the reactivity of the C=C bond in cyclopropanation reactions with diazomethane catalyzed by copper and palladium compounds. The acetal substituents at the α- or γ-position with respect to the C=C bond were found to exert an activating effect on the yields of cyclopropanation products compared to the starting unsaturated carbonyl compounds, which give 1,3-dipolar cycloaddition adducts with CH2N2 as by-products. Cyclopropanation of the double bonds appeared to be most efficiently catalyzed by Pd(acac)2.

Xanthones from a Microfungus of the Genus Xylaria.

Abstract: Chemical investigations of a microfungus Xylaria sp. isolated from the Australian rainforest tree Glochidion ferdinandi have afforded two new natural products, 2-hydroxy-6-methyl-8-methoxy-9-oxo-9H-xanthene-1-carboxylic acid (1) and 2-hydroxy-6-hydroxymethyl-8-methoxy-9-oxo-9H-xanthene-1-carboxylic acid (2). Compound 1 has previously been synthesised but only partially characterised. Methylation of 1 using diazomethane afforded the crystalline compound 2,8-dimethoxy-6-methyl-9-oxo-9H-xanthene-1-carboxylic acid methyl ester (3), whose structure was determined by single crystal X-ray analysis. This paper reports the full spectroscopic characterisation of compounds 1–3 by NMR, UV, IR and MS data. All compounds were inactive in a brine shrimp lethality assay and several antimicrobial screens.

Synthesis of 2-pyrazoline-5-carboxylic acid derivatives using trimethylsilyldiazomethane

Abstract: 1,3-Dipolar cycloaddition reaction of α,β-unsaturated esters, amides or nitriles with diazomethane or trimethylsilyldiazomethane can be one of the powerful methods for the synthesis of pyrazoline building blocks, particularly, 2pyrazoline-5-carboxylic ester (1), amide or nitrile which can be used as chiral precursors in the preparation of several unnatural amino acids (2 and 4) and as building blocks, pyrazoline derivative (3), for the asymmetric synthesis. But, prior studies on the cycloadditions of α,βunsaturated ester with diazoalkanes or trimethylsilyldiazomethane had indicated that the pyrazoline (5) initially formed in such cycloadditions readily isomerized (1,3proton migration) to the corresponding conjugated 2pyrazoline-3-carboxylic ester (6), not to the desired 2pyrazoline-5-carboxylic ester (1) (Scheme 2). Also, reaction of α,β-unsaturated nitrile with trimethylsilyldiazomethane gave the same result (Scheme 3) and so far no single example has been reported for the cycloaddition of diazomethane or trimehtylsilyldiazomethane with α,β-unsaturated amide for the synthesis of 2-pyrazoline-5-carboxamide. These reports prompted us to attempt synthesis of 2pyrazoline-5-carboxylic ester, amide and nitrile through controlling the reaction before 1,3-proton migration. Therefore, under several conditions, we investigated cycloaddition reaction of α,β-unsaturated ester, amide and nitrile with trimethylsilyldiazomethane.

A Tris(carbene) Constructed with Stable Triplet Carbene Units

Abstract: Bis[10-(4-t-butyl-2,6-dimethylphenyl)-9-anthryl]diazomethane, which can generate a fairly stable triplet carbene that can survive for even a week in solution at room temperature, was shown to be st...

Addition of Diazomethane to Phosphonodithioformates and Reactions of Phosphonylated Thiocarbonyl S-Methylides

Abstract: The reaction of phosphonodithioformates 14 with diazomethane at –60°C yielded 2,5-dihydro-1,3,4-thiadiazoles 15 as unstable intermediates. Their structure was evidenced by the base-catalyzed elimination of methylsulfane leading to 1,3,4-thiadiazole-2-phosphonates. At ca. –35°C, thermal decomposition of 15 by N2-elimination led to reactive thiocarbonyl S-methylides 17. In the absence of trapping reagents, these 1,3-dipoles undergo a head-to-head dimerization leading to 1,4-dithianes 18. An intermediate zwitterionic dimer 19 was detected by 31P NMR spectroscopy. The initially formed thiocarbonyl S-methylide 17 as well as an open-chain zwitterionic dimer 20 was intercepted by methanol. Stable interception products were also obtained with S- and N-nucleophiles.

Synthesis and structure of spirocyclic tetrahydrothiophene derivatives bearing a 'cage' residue

Abstract: Trapping of the thiocarbonyl S-methanide 4 with tetracyanoethene and N-methyl-maleimide led to the [3+2]-cycloadducts 11 and 12, respectively. The structures of these cycloadducts were established by X-ray crystallography. The 1,3-dipole 4 has been generated by thermal decomposition of the corresponding 2,5-dihydro-l,3,4-thiadiazole 2, which was prepared by the 1,3-dipolar cycloaddition of diazomethane with thioketone 1.

Emission spectroscopic investigation of triplet diarylcarbene generated in molecular sieve VPI-5.

Abstract: We report an attempt to generate and characterize a triplet carbene, bis(2,4,6-trichlorophenyl)carbene (31), in zeolites Y and L and in a molecular sieve VPI-5 in which a possible dimerization and reaction with the precursor of carbene are significantly retarded, thus making the triplet carbene longer lived than in solution at room temperature. The adsorption of a corresponding diazomethane (1-N2), the precursor of 1, was carefully examined by comparing the absorption spectrum after adsorption with that of 1-N2 in n-pentane, which revealed that 1-N2 was adsorbed with the diazo group intact only in VPI-5, while in other zeolites 1-N2 was found to be decomposed upon adsorption. This difference in reactivity of the hosts was ascribed to the absence of Bronsted-acid sites in VPI-5. The photoirradiation of 1-N2 in VPI-5 at 77 K was monitored by emission spectroscopy, which revealed that bis(2,4,6-trichlorophenyl)methyl radical (1-H) was produced as the only detectable species under these conditions. This is in...

High-level calculations of the enthalpy of formation of diazomethane

Abstract: High-level calculational methods (G2, G3, and several CBS methods) are used to determine the enthalpy of formation of diazomethane, CH 2 N 2 . The results are compared to sparse experimental data.

Unusual Methylene Insertion Reactions

Abstract: Spontaneous and unassisted methylene insertions into S─Cl and Se─S, C─S and C─H bonds as well as S─S and Se─S cleavages, double methylene insertions, and a1, 3-addition to diazomethane, which have been observed in the unaided low temperature reactions of diazomethane with sulfenyl halides and dithio-selenide without the need for the photo-generated carbene moiety.

Generation and [2+3]cycloadditions of a sulfonylated thiocarbonyl S-methanide

Abstract: The sulfonylated thiocarbonyl S-methanide (2a) was generated in situ by addition of diazomethane to the C-sulfonylated dithioformate (1a) and subsequent thermal elimination of nitrogen. This 1,3-dipole was intercepted by C,C- and C,S-dipolarophiles. Whereas in the first case the cycloadducts (10) and (11) could be isolated as stable products, the cycloadducts of type (8), which are the proposed products of the reaction with thioketones, underwent a spontaneous rearrangement to give open-chain ketene dithioacetals (5) and (6).

Sulphur-substituted pyrrolo[3, 4-b]quinolines : synthesis, chemistry and antimicrobial activity

Abstract: Dihydro-2-propyl-3-propylimino-9-thioxo-pyrrolo(3,4-b)quinolin-1-one reacts with an aliphatic primary, secondary or tertiary amine to form a 1:1 substrate:amine (thiolate) complex. It also readily undergoes S-alkylation (with diazomethane or with an alkyl halide), S-acetylation (with acetic anhydride), hydrogenolysis (Raney nickel) with removal of sulphur, and acid-catalysed hydrolysis (with selective replacement of the 3-propylimino function by oxygen). Two novel di-(pyrrolo(3,4-b) quinolinyl) sulphide reaction products are described and their structures established. Treatment of these 'dimers' and related 9-alkylthio-substituted pyrroloquinolines with an aliphatic amine provides a convenient access to 'simple' or 'mixed' 2-alkyl-9-alkylamino-3-alkylimino-pyrroloquinoline derivatives. Preliminary antimicrobial (in vitro) tests indicate that: (a) the weak antimicrobial activity of the aforementioned 9-thioxo-pyrroloquinoline substrate against three selected Gram-positive pathogens is significantly enhanced in its amine complexes, and by the presence of a 6-fluoro atom in the quinoline moiety, and (b) that substitution of the 4-oxo-function in 4-oxo-3-quinolinecarboxylic acids by an ethylimino group leads to a marked reduction in antimicrobial properties.

Synthesis of 2-Pyrazoline-5-carboxylic Acid Derivatives Using Trimethylsilyldiazomethane.

Abstract: 1,3-Dipolar cycloaddition reaction of α,β-unsaturated esters, amides or nitriles with diazomethane or trimethylsilyldiazomethane can be one of the powerful methods for the synthesis of pyrazoline building blocks, particularly, 2pyrazoline-5-carboxylic ester (1), amide or nitrile which can be used as chiral precursors in the preparation of several unnatural amino acids (2 and 4) and as building blocks, pyrazoline derivative (3), for the asymmetric synthesis. But, prior studies on the cycloadditions of α,βunsaturated ester with diazoalkanes or trimethylsilyldiazomethane had indicated that the pyrazoline (5) initially formed in such cycloadditions readily isomerized (1,3proton migration) to the corresponding conjugated 2pyrazoline-3-carboxylic ester (6), not to the desired 2pyrazoline-5-carboxylic ester (1) (Scheme 2). Also, reaction of α,β-unsaturated nitrile with trimethylsilyldiazomethane gave the same result (Scheme 3) and so far no single example has been reported for the cycloaddition of diazomethane or trimehtylsilyldiazomethane with α,β-unsaturated amide for the synthesis of 2-pyrazoline-5-carboxamide. These reports prompted us to attempt synthesis of 2pyrazoline-5-carboxylic ester, amide and nitrile through controlling the reaction before 1,3-proton migration. Therefore, under several conditions, we investigated cycloaddition reaction of α,β-unsaturated ester, amide and nitrile with trimethylsilyldiazomethane.

Stanovení kyseliny adipové v prubehu její polykondenzace s 1,4-diaminobutanemM

Abstract: A method for determination of adipic acid in the product of its polycondensation with butane-1,4-diamine in aqueous medium has been developed. The acid is isolated from the reaction mixture by liquid-liquid extraction, then derivatized with diazomethane and the resulting dimethyl ester is analyzed by GLC. The presence of water does not influence the analysis. The method can be used for determination of the adipic acid in the reaction mixture ranging from 0.5 to 100 %.

Interaction of diazomethane derivatives with 3,4-dimethoxyacetophenone and effect of triphenylphosphine presence on the products nature

Abstract: 3,4-Dimethoxyacetophenone reacts with 2-diazo-1,3-hydrindenedione, diphenyldiazomethane and 9-diazofluorene in chlorobenzene to give four, five and six membered rings. Further, the latter compounds react with triphenylphosphine to give five and six membered ring products. The structures of the reaction products are confirmed by IR, NMR and mass spectra, as well as by some chemical tests.

The First Example of Catalytic Aziridination Mediated by Arsonium Ylides: Preparation of trans‐Pentafluorophenyl‐Containing Aziridines.

Abstract: Triphenylarsine catalyzes the formation of aziridines from tosyl imines and aromatic diazo compounds in a one-pot reaction. It is the first example of catalytic aziridination mediated by arsonium ylides. It gave aziridines in excellent diastereoselectivity with pentafluorophenyl diazomethane as the substrate. This catalytic reaction is complementary with the reaction mediated by sulfur ylides.