Stabilization of proline enamine carboxylates by amine bases

As part of our ongoing studies to provide an experimental basis for the improved understanding of organocatalytic reaction mechanisms we present a study on the influence of amine bases on enamine intermediate stabilization in proline catalysis. The (partial) deprotonation of the proline acid function is displayed by characteristic shifts of certain proton resonances and is also manifested by an increase of the amount of enamine intermediate upon reaching a critical pK(aH). Strong bases, such as 1,8-diazabicyclo[5.4.0]-undec-7-ene (DBU), allow for outstanding enamine stabilization in various solvents and, hence, permit the detection of enamine species that have been inaccessible until now (illustrated by the observation of minor amounts of Z enamines). The in situ NMR detection of a prolinate-DBUH(+) ion pair supports the well-documented reversal of enantioselectivity of proline-catalyzed aminations in the presence of amine bases by disabling the bifunctional activity and switching to a "simple" stereocontrol effect (as known from the J?rgensen/Hayashi-type diarylprolinol ethers). In addition, the possibility of attractive ionic interactions between both the iminium ion and prolinate enamines available in the presence of strong amine bases suggests promotion of the Mannich pathway in aldol reactions to mainly form condensation products.     

Synthesis,characterization and antibacterial properties of Schiff bases and Schiff base metal complexes derived from 2,3-diamino- pyridine

New copper(II), zinc(II) and nickel(II) Schiff base complexes derived from 2,3-diaminopyridine (DAPY) and selected aldehydes, namely salicylaldehyde (SalH), 4-hydroxybenzaldehyde (4-OHBenz) and 4-nitrobenzaldehyde (4-NO₂Benz), and one mixed Schiff base, DAPY-{4-OHBenz}{SalH} were prepared and characterized by a combination of elemental analyses, i.r. and n.m.r. spectra, and magnetic susceptibility measurements. The Schiff bases and some of the metal complexes display antibacterial properties.     

Carbon-nitrogen bond cleavage in pyridine ring systems mediated by organometallic thorium(IV) complexes

Thorium(IV) alkyl and aryl complexes of the type (C(5)Me(5))(2)ThR(2)(R = CH(2)Ph, Ph) have been found to mediate the facile ring-opening and dearomatization of the pyridine ring of pyridine N-oxide under ambient conditions to afford the first thorium eta(2)-(O,N)-oximate complexes.     

Lanthanide-promoted ethylation of Schiff bases by triethylaluminum

[reaction: see text] Schiff bases of aromatic aldehydes and anilines that fail to react with triethylaluminum are smoothly alkylated at room temperature in the presence of lanthanide catalysts. The alkylation takes place selectively at the vinylic carbon atom.     

Formation of a benzimidazole ring accompanied by the cleavage of a nitrogen-carbon bond

The reaction of thionyl chloride with arylamides of aromatic acids, which usually gives rise to stable imidoyl chlorides, leads in the case of N-(o-dimethylaminophenyl)benzimide and N-(o-piperidinophenyl)-benzimide to the formation of a benzimidazole ring, which is accompanied by the cleavage of the nitrogen-carbon bond. This reaction and the reaction of chloral oxime with o-dialkylaminoanilines studied previously, which also leads to the formation of a benzimidazole ring, are compared with the Braun reaction. It has been shown that when thionyl chloride reacts with N-(o-dimethylaminophenyl)isonitrosoacetamide, no formation of a benzimidazole ring takes place and only N-(o-dimethylaminophenyl)carbamoyl cyanide is formed.     

Novel mesomorphic Schiff bases

2-(4-Alkoxybenzylideneamino)-4-[(4-nitrophenyl)amino]thiazoles have been synthesized. They show nematic type enantiotropic mesomorphism in the range 41–184°C. Bashkir State University, Ufa 450074. Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 11, pp. 1559–1560. November, 1997.     

New immobilized Schiff bases

In this study, three new immobilized Schiff bases and their Co(II), Cu(II) and Ni(II) metal complexes have been prepared. The ligands silica-Si[N-(3-propyl)2,4-dihydroxybenzaldimine] (1) H₂L, silica-Si[N-(3-propyl)4-methylsalicylaldimine-3-methoxy] (2) HL and silica-Si[N-(3-propyl)2-pyridinecarboxyaldimine] (3) L have bidentate characters. Therefore, the complexes are the mononuclear. Ligands and metal complexes were characterized by FTIR, AAS and thermoanalytical techniques. On the basis of analytical data and IR studies, a 1:1 metal to ligand stoichiometry has been suggested. TG and DTA results showed that these ligands and complexes had good thermal stability. The heat capacities of ligands were reported in the temperature range 273–363 K as no thermal anomaly was found in this temperature range.     

Solid-state synthesis of Schiff bases

A new preparative method for the synthesis of Schiff bases by the solid-state interaction of crystalline organic and organometallic aldehydes and amines is suggested. The possibility of direct synthesis of aldimines in the solid state from amine salts without isolation of the free amines is demonstrated. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 11, pp. 2056–2059, November, 1997.     

Complexes of hydrazide Schiff bases

Summary 1,2-Diphenyl-2-(benzoylhydrazino)ethanol (DBE) and 1,2-diphenyl-2-(p-nitrobenzoylhydrazino)ethanol (DPNBE) form complexes of general formulae [M(H₂L)₂]X₂ and [M₂L₂] (where M = Co or Ni, H₂L and L are the neutral and dibasic forms of the ligands and X = Cl or NO₃). The analytical, spectral, magnetic and physical studies show the complexes to be of two types, namely monomeric cationic species prepared in neutral media and neutral binuclear oxygen-bridged species formed in alkaline solution. The ligands are tridentate, coordinating through carbonyl (or enolic) oxygen, azomethine nitrogen and alcoholic oxygen atoms.     

Formation of aromatic rings through enamine annulation

Condensation of pyrrolidine enamine of ketones with 1, 4-diacetoxy-2-butanone provides a new, concise synthetic route to substituted benzenes, dihydroindenes, tetrahydronaphthalenes, and di- and octahydrophenanthrenes. The reaction produced modest yields with regiocontrol of the secondary amine substituent.     

Reaction of trialkylboranes with 2-bromo-6-lithiopyridine: Stereospecific alkylative cleavage of pyridine ring

Reaction of 2-bromo-6-lithiopyridine with trialkylboranes affords 5-alkyl-5-dialkylboryl-2-(Z), 4(E)- pentadienenitriles by stereospecific alkylative cleavage of the pyridine ring. These intermediary vinylboranes are versatile reagents for the preparation of 5-alkyl-2(Z), 4(E)-pentadienenitriles, 5,5-dialkyl-4-pentenenitriles and 5,5-dialkyl-2,4-pentadienenitriles.     

Synthesis of Schiff bases by condensation of hetarylcarboxaldehydes withp-phenetidine

Summary Treatment of quinolinecarboxaldehydes and their derivatives withp-ethoxyaniline yields in a one-step reaction a series of new Schiff bases in 47–73% yield. The products [quinoline-2-, 6-methylquinoline-2-, quinoline-4-, quinoline-8-, and acridine-9-N-(p-ethoxyphenyl)formimidoyl], have been fully characterized.

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Synthese von Schiffschen Basen durch Kondensation von Hetarylaldehyden mitp-Phenetidin

Zusammenfassung Umsetzung von Chinolinaldehyden und deren Derivaten mitp-Ethoxyanilin liefert in einer Einstufenreaktion neue Schiffsche Basen in 47–73%iger Ausbeute. Alle Produkte [Chinolin-2-, 6-Methylchinolin-2-, Chinolin-4-, Chinolin-8- und Acridin-9-N-(p-ethoxyphenyl)formimidoyl] wurden voll charakterisiert.

     

Formation of new 4-isocyanobut-2-enenitriles by thermal ring cleavage of 3-pyridyl azides

A new thermal ring cleavage of 3-pyridyl nitrenes for the formation of 4-isocyanobut-2-enenitrile products is reported. Thermolysis of 4-(thien-3-yl)-3-pyridyl azide 1 and 3-azido-4-(1-TIPS-1H-pyrrol-3-yl)pyridine 5 afforded two new isonitrile-nitrile products by ring cleavage; 4-isocyano-2-(thiophen-3-yl)but-2-enenitrile (3, 27%) and 4-isocyano-2-(1-TIPS-1H-pyrrol-3-yl)but-2-enenitrile (7, 20%), in addition to our previously reported pyrido[3,4-b]thienopyrrole (2, 29%) and pyrido[3,4-b]pyrrolo[3,2-d]pyrrole (6, 71%) products. Minor amounts of 2-(thien-3-yl)-1H-pyrrole-3-carbonitrile (4, 6%), formed by ring contraction, were also isolated after thermolysis of azide 1. Isonitriles 3 and 7 underwent degradation into amine 3b and formamide 7a by acidic hydrolysis. The nature and chemistry of compounds 3, 4 and 7 were investigated.     

Expansion of a pyridine ring by a nitrene

Pyrolysis of 2-(o-azidobenzyl)pyridine (3) gives 3H-1,2-diazepino[1,7-a]indole (5), in which the intermediate nitrene has expanded the pyridine ring.     

Reaction of antipyrine with Schiff bases

New dihydropyrazolone derivatives were prepared by condensation of antipyrine with substituted arylmethyleneanilines or arylmethylene-2-naphthylamines.     

Solvent extraction of metal ions by use of Schiff bases

Schiff bases are aldehyde or ketone like compounds in which the carbonyl group is replaced by imine or azomethine group. They are widely used for industrial purposes and also exhibit a broad range as extractants. A general view of solvent extraction applications of complexes is discussed in this review. The family of Schiff bases and their extraction of various transition metals such as Co, Cu, Cr, Fe, Ga, Hg, Mn, Mo and Ni are discussed. A brief history of the synthesis and reactivity of Schiff bases will be presented. Factors on solvent extraction will be illustrated and discussed.     

Reaction of dihydrosylvan with Schiff bases

Summary In the presence of Lewis acids (BF₃, AlCl₃, AlBr₃), dihydrosylvan (2-methyl-4,5-dihydrofuran) reacts with Schiff bases, like o-nitrobenzylideneaniline, o-hydroxybenzylideneaniline, benzylidene-o-aminophenol, cinnamaldehyde anil, citral anil and cyclohexanone anil, to give tetrahydrofuranotetrahydroquinoline derivatives as adducts.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 9, pp. 1693–1695, September, 1964