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1.
Three pairs of diastereomeric piperidines, cis- and trans-2-methylpiperidine-3-carboxylate (6a and 6b), cis- and trans-2-methylpiperidine-3-carboxylamide (9a and 9b) and cis- and trans-2-methyl-3-cyanopiperidine (11a and 11b), were synthesised for the purpose of investigating the effect of the axial versus equatorial carboxylate, carboxamide and cyano group on piperidine base strength. The pKa values of the six compounds were determined to be 11.0 (6a), 10.4 (6b), 9.5 (9a), 9.3 (9b), 7.8 (11a) and 8.0 (11b). This shows that the strong electron-withdrawing effect of the cyano group and the effect of the amide group are relatively independent of spacial orientation. The carboxylate, on the other hand is considerably less electron-withdrawing when axial.  相似文献   

2.
A direct link between the Passerini reaction and α-lactams   总被引:1,自引:0,他引:1  
István Lengyel 《Tetrahedron》2004,60(5):1107-1124
α-Lactams (aziridinones) can function to replace two of the three reactants, the oxo-compound and the isonitrile, in the Passerini reaction. Four α-lactams (5a-d) were reacted with mono- and dicarboxylic acids of positive pKa values to give 2-acyloxycarboxamides (4) and bis-2-acyloxycarboxamide products 12 and 13, respectively. The same compounds were also prepared via the Passerini reaction. Acids with a negative pKa decarbonylate α-lactams to give immonium salts. The main path of the reaction depends on the pKa of the acid component, the reactivity of the α-lactam, and the reaction conditions.  相似文献   

3.
The UV–vis spectra of recently synthesized 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-one, (I), and 5-benzoyl-1-(methylphenylmethyleneamino)-4-phenyl-1H-pyrimidine-2-thione, (II) were studied in aqueous methanol (5%, v/v methanol). The nature of the electronic transitions and the roles of carbonyl oxygen of I and thiocarbonyl sulfur of II on the behavior of UV–vis spectra were discussed.Acid–base equilibria of the compounds against varying pH and pKa values related equilibria were determined at an ionic strength of 0.10 M by using the Henderson–Haselbalch equation. The mean acidity constants for the protonated forms of the compounds were determined as pKa1 = 5.121, pKa2 = 7.929 and pKa3 = 11.130 for I and pKa1 = 4.684, pKa2 = 7.245 and pKa3 = 10.630 for II. The preferred dissociation mechanisms were discussed based on UV–vis data and a mechanism was proposed for each compound.  相似文献   

4.
Bis(p-substituted benzoylmethyl)tellurium dibromides, (p-YC6H4COCH2)2TeBr2, (Y=H (1a), Me (1b), MeO (1c)) can be prepared either by direct insertion of elemental Te across CRf-Br bonds (where CRf refers to α-carbon of a functionalized organic moiety) or by the oxidative addition of bromine to (p-YC6H4COCH2)2Te (Y=H (2a), Me (2b), MeO (2c)). Bis(p-substituted benzoylmethyl)tellurium dichlorides, (p-YC6H4COCH2)2TeCl2 (Y=H (3a), Me (3b), MeO (3c)), are prepared by the reaction of the bis(p-substituted benzoylmethyl)tellurides 2a-c with SO2Cl2, whereas the corresponding diiodides (p-YC6H4COCH2)2TeI2 (Y=H (4a), Me (4b), MeO (4c)) can be obtained by the metathetical reaction of 1a-c with KI, or alternatively, by the oxidative addition of iodine to 2a-c. The reaction of 2a-c with allyl bromide affords the diorganotellurium dibromides 1a-c, rather than the expected triorganotelluronium bromides. Compounds 1-4 were characterized by elemental analyses, IR spectroscopy, 1H, 13C and 125Te NMR spectroscopy (solution and solid-state) and in case of 1c also by X-ray crystallography. (p-MeOC6H4COCH2)2TeBr2 (1c) provides, a rare example, among organotellurium compounds, of a supramolecular architecture, where C-H-O hydrogen bonds appear to be the non-covalent intermolecular associative force that dominates the crystal packing.  相似文献   

5.
《Polyhedron》1999,18(23):3057-3064
The synthesis of new cyclometalated compounds of palladium(II) with the mixed-donor bidentate ligands o-Ph2PC6H4–CH=NR is described. Two series of complexes [Pd(C^N)(o-Ph2PC6H4–CH=NR)][PF6] have been prepared using either azobenzene or 2-phenylpyridine as cyclometalated ligands [C^N=azobenzene (azb); R=Me (1a), Et (2a), nPr (3a), iPr (4a), tBu (5a), Ph (6a), NH–Me (7a); C^N=2-phenylpyridine (phpy); R=Me (1b), Et (2b), nPr (3b), iPr (4b), tBu (5b), Ph (6b), NH–Me (7b)]. The new complexes were characterized by partial elemental analyses and spectroscopic methods (IR, FAB, 1H and 31P NMR). The molecular structures of compounds 2a (monoclinic, P 21/n) and 1b (monoclinic, C 2/c) have been determined by a single-crystal diffraction study. In both cases this technique revealed the relative trans configuration between the phosphorus atom and the nitrogen atom of the ortho-metalated ligand.  相似文献   

6.
Condensation of the O-protected hydroxyferrocene carbaldehyde (Sp)-1 with suitable diamines, followed by liberation of the hydroxyferrocene moiety leads to a new type of ferrocene-based salen ligands (3). While the use of ethylenediamine in the condensation reaction yields the planar-chiral ethylene-bridged ligand [(Sp,Sp)-3a], reaction with the enantiomers of trans-1,2-cyclohexylendiamine gives rise to the corresponding diastereomeric cyclohexylene-bridged systems [(S,S,Sp,Sp)-3b and (R,R,Sp,Sp)-3c], which feature a combination of a planar-chiral ferrocene unit with a centrochiral diamine backbone. Starting with the ferrocene-aldehyde derivative (Rp)-1, the enantiomeric ligand series (3d/e/f) is accessible via the same synthetic route.The (Sp)-series of these newly developed N2O2-type ligands was used for the construction of the corresponding mononuclear bis(isopropoxy)titanium (4a/b/c), methylaluminum (5a/b/c) and chloroaluminum-complexes (6a/b/c), which were isolated in good yields and identified by X-ray diffraction in several cases. The aluminum complexes (5/6) were successfully used in the Lewis-acid catalyzed addition of trimethylsilylcyanide to benzaldehyde, yielding the corresponding cyanohydrins in 45-62% enantiomeric excess.  相似文献   

7.
Carmine Gaeta  Placido Neri 《Tetrahedron》2008,64(22):5370-5378
Water-soluble p-sulfonatocalix[7]arene 1 has been synthesized in good yield through standard procedures and its conformational preferences have been investigated by Monte Carlo conformational searches. The acid-base properties of 1 were investigated by means of potentiometric titration, obtaining pKa values in agreement with those reported for other p-sulfonatocalix[n]arene homologs. The binding ability of 1 toward organic quaternary ammonium cations such as Diquat (2), Paraquat (3), and Chlormequat (4) was investigated by means of 1H NMR titrations in D2O at pD=7.3, DOSY NMR measurements, and 2D ROESY NMR spectroscopy. Spectrofluorimetry proved to be a useful method for the determination of trace amounts of 2 and 3 in aqueous solution by using Acridine Orange bound to 1 as a chemical indicator.  相似文献   

8.
The influence of substitution of amidine group on tautomeric equilibria constants and basicities is discussed. Equations based on correlation analysis methods are derived enabling predictions of both, microscopic pKa, values of individual tautomers, measured macroscopic pKa values of the tautomeric mixture, as well as the tautomeric equilibrium constant (as pKT). It is shown that pKarn values of unsymmetrically N,N'-disubstituted amidines should obey a non-linear relation with σ° constants, and only for symmetrically N,N'-disubstituted amidines obey the linear Hammett equation. Tautomeric equilibrium constants of N,N'-disubstituted amidines correlate withσ° substituent constants. The methods of prediction of pKa value of both tautomers and pKT value are proposed.Derived relations are applied to the series of N,N'-diphenylacetamidines and benzamidines.  相似文献   

9.
A series of chiral C1- and C2-symmetric ferrocenyl Schiff bases (1a-c), ferrocenyl aminoalcohols (2a), ferrocenylphosphinamides (2b-c), 1,1′-ferrocenyl-diol (3), and 1,1′-ferrocenyl-disulfonamide (4) were prepared and employed as base catalysts or as ligand for titanium(IV) complexes in the asymmetric addition of diethylzinc to aromatic aldehydes. High enantioselectivity up to almost 100% ee was achieved for the alkylation of benzaldehyde and p-methoxybenzaldehyde with 1 or 3. In contrast, however, the β-aminoalcohol (2a) and phosphinamides (2b and c) that are ubiquitous classes of base catalysts for this reaction proved inefficient in our hands, regardless of the types of substrates or reaction conditions. Comparative studies show that there exist various reaction parameters governing not only chemical yields but also optical yields. These include steric and electronic environment of the substrate, the solvent, the reaction temperature, and the nature of the ferrocene moieties.  相似文献   

10.
From the reaction of 6-(p-methoxyphenyl) fulvene (1a), 6-(3,4-dimethoxyphenyl) fulvene (1b) and 6-(3,4,5-trimethoxyphenyl) fulvene (1c) with LiBEt3H, lithiated cyclopentadienide intermediates (2ac) were synthesised. These intermediates were then transmetallated to vanadium with VCl4 to yield the benzyl-substituted vanadocenes bis-[(p-methoxybenzyl)cyclopentadienyl] vanadium(IV) dichloride (3a), bis-[(3,4-dimethoxybenzyl)cyclopentadienyl] vanadium(IV) dichloride (3b), and bis-[(3,4,5-trimethoxybenzyl)cyclopentadienyl] vanadium(IV) dichloride (3c). The two vanadocenes 3a and 3c were characterised by single crystal X-ray diffraction. All three vanadocenes had their cytotoxicity investigated through MTT based preliminary in vitro testing on the LLC-PK (pig kidney epithelial) cell line in order to determine their IC50 values and compare them with the corresponding titanocene dichloride derivatives. Vanadocenes 3bc were found to have IC50 values of 9.1 and 8.3 μM, while 3a showed a superior value of 3.0 μM, respectively.  相似文献   

11.
The solvent-free reactions of fullerenes and N-alkylglycines with and without aldehydes (RCHO) 2a-e under high-speed vibration milling (HSVM) conditions have been investigated. Fulleropyrrolidines 4a-e (C60(CH2N(CH3)CHR), R=H (4a), C6H5 (4b), p-NO2-C6H4 (4c), p-CH3O-C6H4 (4d), p-(CH3)2N-C6H4 (4e)) were obtained in moderate yields from reactions of C60 with aldehydes 2a-e and N-methylglycine (Prato reaction). In all these solvent-free reactions, 4a was found to be formed besides 4b-e, indicating that fullerenes can react with N-substituted glycines in the absence of aldehyde to give fulleropyrrolidines. For this novel reaction, a possible reaction mechanism involving an electron transfer process has been proposed. Intrigued by this observation, the dependence of the yield on the reagent ratio for the reaction of C60 with paraformaldehyde and/or N-methylglycine was examined to search the optimal conditions. The reaction of C70 with paraformaldehyde and/or N-methylglycine under HSVM conditions was also studied and was found to give the positional isomers of [70]fulleropyrrolidines.  相似文献   

12.
The polarographic behaviour of phenylhydrazonomesoxalonitrile (2) and ethyl phenylhydrazonomesoxalonitrile (3) as well as pK′ and pKa values are reported for a series of arylhydrazones of α-cyanoketones.  相似文献   

13.
The synthesis and full characterization of a number of amino acid and dipeptide derivatives with sulfur-containing side chains derived from ferrocene carboxylic acid and ferrocene-1,1′-dicarboxylic acid is presented. In particular, compounds Fc-CO-(Aaa)n-OMe (4) and Fe[C5H4-CO-(Aaa)n-OMe]2 (3) with (Aaa)n = Cys(Bzl) (a), Cys(Bzl)-Cys(Bzl) (b), Cys(p-OMe-Bzl) (c), Cys(p-OMe-Bzl)-Cys(p-OMe-Bzl) (d), Met (e), and Met-Met (f) were prepared. Also, the free acid derivatives Fe[C5H4-CO-Met-OH]2 (6e) and Fc-CO-Met-OH (7e) were prepared and characterized. The solid state structures of 3a, 4b, and 4e were determined by single crystal X-ray diffraction. Compound 3a shows a 1,3′ substitution pattern on the Cp rings in the solid state. Structures in solution were determined by NMR, IR and CD spectroscopy, with particular emphasis on the question of hydrogen bonding and helical chirality of the metallocene. As an example, the full assignment for the Cp signals in the disubstituted derivative 3a was achieved by simulation of the 1H NMR signals from the cyclopentadienyl ring in combination with 2D-NOESY spectra. In solution, 3a has the known 1,2′ substitution pattern, which is stabilized by intramolecular hydrogen bonds.  相似文献   

14.
Attempted detosylation of the 3-amino-1-(p-tosylamino)indole-2-carbonitriles 4a-c using either K2CO3 in EtOH or DBU in PhH at reflux gives unexpectedly the 3-(N-p-tosylamino)indole-2-carbonitriles 5a-c, respectively in high yields. Nevertheless, treatment of 1-(p-tosylamino)indoles 4a-c with thiophenol and DBU in PhH at reflux gives the detosylated 3-aminoindole-2-carbonitriles 5a-c. Reaction mechanisms supporting the tosyl migration (4→5) and the reductive detosylation (4→2) are proposed. All new compounds are fully characterised.  相似文献   

15.
Molybdenum-95 NMR chemical shifts are reported for a series of Mo(O) compounds of the type Mo(CO)4(pip)2−nLn(n = 1,2; L = substituted pyridine ligands). The σ(95Mo) values correlate well with the pKa values for the substituted pyridines; for the n = 1 series, σ (95Mo) ranges from − 1053 ppm (pKa = 1.86 for 4-CN) to − 1120 ppm (pKa = 9.61 for 4-NMe2). The effects of solvent polarity and some in situ reactivity studies are described and the nature of the MoL bond compared to that with piperidine and some other ligands is discussed.  相似文献   

16.
Acid?Cbase equilibria of the aqua adducts of Ru(II) arene complexes, general formulae [(??6-p-cymene)Ru (L1?3)Cl2] where L1?=?3-acetylpyridine (1), L2?=?4-acetylpyridine (2) and L3?=?2-amino-5-chloropyridine (3), then [(??6-p-cymene)Ru(HL4)Cl2] with HL4?=?isonicotinic acid (4); [(??6-p-cymene)Ru(HL5?8)Cl] where H2L5?=?2,3-pyridine dicarboxylic acid (5), H2L6?=?2,4-pyridine dicarboxylic acid (6), H2L7?=?2,5-pyridine dicarboxylic acid (7) and H2L8?=?2,6-pyridine dicarboxylic acid (8) have been studied. pK a values were determined by potentiometry at 25?°C and constant ionic strength of 0.1?M NaNO3. The assumed equilibria were confirmed by UV and 1H-NMR spectroscopy.  相似文献   

17.
Kuang Shen  Jia-Ning Li 《Tetrahedron》2007,63(7):1568-1576
A first-principle method has been successfully developed for the prediction of pKa values of aromatic heterocyclic compounds in DMSO solution with a precision of 1.1 pKa units. Comparison of theoretical results and experimental data (where available) also shows excellent consistency. Armed with this useful approach, the pKa values for a series of aromatic heterocycles were calculated in DMSO. Moreover, a discussion of the relationships between hydrogen acidities and molecular structures is conducted for the first time (determinants of C-H acidities, substituent effects, and some practical use of dehydrometalation). These statistics could be useful for synthetic chemists to design proper routes for introduction of aromatic heterocyclic moiety, especially when dehydrometalation reactions are used.  相似文献   

18.
This work reports on the preparation of the complexes [PdCl2(Y1)2], [PdCl2(Y2)2] (Y1 = (p-tolyl)3PCHCOCH3 (1a); Y2 = Ph3PCHCO2CH2Ph (1b)), [Pd{CHP(C7H6)(p-tolyl)2COCH3}(μ-Cl)]2 (2a), [Pd{CHP(C6H4)Ph2CO2CH2Ph}(μ-Cl)]2 (2b), [Pd{CH{P(C7H6)(p-tolyl)2}COCH3}Cl(L)] (L = PPh3 (3a), P(p-tolyl)3 (4a)) and [Pd{CH{P(C6H4)Ph2}CO2CH2Ph}Cl(L)] (L = PPh3 (3b), P(p-tolyl)3 (4b)). Orthometallation and ylide C-coordination in complexes 2a4b are demonstrated by an X-ray diffraction study of 4a.  相似文献   

19.
Uracil-annulated heteroazulenes, 6-substituted 7,9-dimethylcyclohepta[b]pyrimido[5,4-d]pyrrole-8(7H),10(9H)-dionylium tetrafluoroborates 7a,b·BF4, which are the isoelectronic compounds of 5-dezazaflavin, were synthesized. X-Ray crystal analysis and MO calculations were carried out to clarify the structural characteristics of 7a,b·BF4. The stability of cations 7a,b is expressed by the pKR+ values which were determined spectrophotometrically to be 10.9 and 11.2, respectively. The electrochemical reduction of 7a,b exhibited high reduction potentials at −0.84 and −0.87 (V vs Ag/AgNO3) upon cyclic voltammetry (CV). A good linear correlation between the pKR+ values and reduction potentials (E1red) of 7a,b·BF4 and reference compounds 4·BF4 and 5·BF4 was obtained. In a search of the reactivity, reactions of 7a,b·BF4 with some nucleophiles, hydride and diethylamine, were carried out to clarify that the introduction of nucleophiles to give regio-isomers is dependent on the nucleophile. The photo-induced oxidation reactions of 7a,b·BF4 toward some alcohols under aerobic conditions were carried out to give the corresponding carbonyl compounds in more than 100% yield [based on compounds 7a,b·BF4], suggesting the oxidizing function of 7a,b·BF4 toward alcohols in the autorecycling process.  相似文献   

20.
A new class of azobenzene-based chelators, trans-3a and trans-3b (3a and 3b), were designed and synthesized in two steps. Both 3a and 3b were readily dissolved in a buffer solution at physiological pH. The values of the dissociation constant of 3a and 3b for Mg2+ and Ca2+ were determined by the Hills plot; KdMg=1.12 mM and KdCa=660 μM for 3a and KdMg=158 μM and KdCa=200 μM for 3b, respectively. On irradiation at 489 nm light, 3a isomerized to give cis-form, which underwent cis-to-trans thermal isomerization in darkness at room temperature. The change in the absorption spectrum of the irradiated solution of 3a in the presence of Mg2+, showing the cis-to-trans thermal isomerization, indicates that the affinity of cis-3a for Mg2+ is lower than that of 3a.  相似文献   

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