Nitropyridines,their synthesis and reactions

Reaction of pyridine and substituted pyridines with N₂O₅ in an organic solvent gives the N‐nitropyridinium ion. When this is reacted with SO₂/HSO₃‐ in water, 3‐nitropyridine is obtained (77 % yield). With substituted pyridines the method gives good yields for 4‐substituted and moderate yields for 3‐substituted pyridines. The reaction mechanism is not an electrophilic aromatic substitution but one in which the nitro group migrates from the 1‐position to the 3‐position by a [1,5] sigmatropic shift. From 3‐nitropyridine, 5‐nitropyridine‐2‐sulfonic acid is formed in a two step reaction. From this, a series of 2‐substituted‐5‐nitropyridines has been synthesized. 3‐Nitropyridine and 4‐substituted‐3‐nitropyridines have been substituted with ammonia and amines by the vicarious nucleophilic substitution (VNS) method with ammonia and amines and by the oxidative substitution method in the position para to the nitro group. High regioselectivities and yields have been obtained in both cases to afford a series of 4‐substituted‐2‐alkylamino‐5‐nitropyridines. The VNS method has also been used in alkylation reactions with 3‐nitropyridines to form dichloromethyl‐and alkoxycarbomethyl‐β‐nitropyridines. From the appropriate substituted nitropyridines imidazopyridines and azaindoles have been formed.     

Beiträge zur Chemie der Si-N-Bindung,XVIII [1]. Über lineare,cyclodisilazan-modifizierte Oligosiloxane

Linear oligosiloxanes with cyclodisilazane rings built into the siloxane chain were prepared by the reaction of hydroxysilyl substituted cyclodisilazanes in the form of their lithiumsilanolates with dimethyldichlorosilane, α,ω-chlorosiloxanes or dimethylchlorosilyl substituted cyclodisilazanes.     

Facile synthesis of highly substituted 3-aminofurans from thiazolium salts, aldehydes, and dimethyl acetylenedicarboxylate

[reaction: see text] A facile preparation of 3-aminofuran derivatives via multicomponent reactions of thiazole carbenes, aldehydes, and dimethyl acetylenedicarboxylate (DMAD) is reported. In this process, the thiazole carbenes, generated in situ from thiazolium salts, reacted with aldehydes and DMAD at -78 to 0 degree C in CH(2)Cl(2) to afford the substituted furans in moderate to good yields. Eight substituted thiazolium salts were employed as carbene precursors in the reaction. Besides aryl aldehydes, alpha,beta-unsaturated aldehydes, aliphatic aldehydes, and arenedial were also investigated and found to be applicable to this reaction.     

Generation of ketone dilithio α,β-dianions and their reactions with electrophiles

Ketone dilithio α,β- and α,β′-dianions can be generated by a tin-lithium exchange reaction of the lithium enolate of β-tributyltin substituted ketones. A chelation-aided approach, which employs β-dichlorobutyltin substituted ketones and n-BuLi, is also useful for the generation of ketone α,β-dianions having the Z-geometry at the alkene. The generated dianions can be transformed into substituted ketones by reaction with various carbon electrophiles.     

Chemo-, regio-, and enantioselective Pd-catalyzed allylic alkylation of indolocarbazole pro-aglycons

[reaction: see text] Monosubstituted isomerically pure indolopyrrolocarbazole precursors have been prepared via palladium-catalyzed asymmetric allylic alkylation methodology, employing both achiral cyclopentenyl electrophiles and chiral glycal derivatives. Chemoselective allylation of (bis)indole lactam pro-aglycon 3 allows access to N-distally substituted indolopyrrolocarbazole derivatives; glyoxamide precursor 14 provides entry into N-proximally substituted derivatives.     

Oxazolidinone-promoted, torquoselective Nazarov cyclizations

Oxazolidinones are powerful promoters of the Nazarov reaction, enabling the cyclization of conventionally resistant substrates to be achieved under mild conditions. They exert excellent regio- and torquoselective control in both the conventional Nazarov reaction giving cyclopentenones and in the "interrupted" Nazarov reaction, giving more highly substituted multistereocenter containing products.     

A One Pot,Facile, and Convenient Synthesis of Some Coumarin Derivatives

Protonation of the reactive 1:1 intermediate produced in the reaction between triphenylphosphine and dimethyl acetylenedicarboxylate by substituted phenols lead to vinyl triphenylphosphonium salt, which undergoes aromatic electrophilic substitution reaction with the phenolate conjugated base to produce coumarin derivatives.     

Photopolymerization V. Unsensitized solution photocyclopolymerization of N,N ′-alkylenebismaleimides

The term, “photopolymerization,” is defined as a polymerization process in which every chain-propagating step involves a photo-chemical reaction. This type of polymerization is exemplified by the unsensitized solution photocyclopolymerization of several N,N ′-alkylenebismaleimides, substituted at the double bond. N,N ′-Alkylenebismaleimides substituted with a bromine atom or two methyl groups at their double bond produce high polymeric products upon ultraviolet irradiation in solution. A general reaction scheme for the photopolymerization is proposed. Kinetic measurements show that the solution photopolymerization of substituted bismaleimides is a multistep reaction.     

Triazole-gold (TAAu) catalyzed three-component coupling (A3 reaction) towards the synthesis of 2, 4-disubstituted quinoline derivatives

A gold-catalyzed three-component coupling reaction (A3 reaction) was developed as an efficient approach for the synthesis of challenging 2,4-disubstituted quinoline derivatives. Compared to previously reported Cu/Au bi-catalyst system, this protocol enables achieving A3 reaction only in the presence of triazole-gold catalyst. Notably, 4-alkyl substituted or 2-alkyl substituted quinoline derivatives were obtained with good yields, which highlighted the unique advantage of this new strategy.     

Facile,eco-friendly,one-pot protocol for the synthesis of indole-imidazole derivatives catalyzed by amino acids

An efficient, convenient green approach for the synthesis of indole-based 2,4,5-trisubstituted and 1,2,4,5-tetrasubstituted imidazoles by multicomponent reaction of substituted 2-arylindole-3-carbaldehydes, benzil, substituted anilines, and ammonium acetate using catalytic amino acid (glycine) in ethanol is described. Several amino acids have also been evaluated as organic catalysts for these reactions. The structures of the compounds have been established on the basis of infrared, mass, and ¹H NMR spectral data. The mild reaction conditions, inexpensive/economical reagents, and good yield show the usefulness of this approach.     

S-, S,S-, S,S,S- Und N,S-Substituierte Dienverbindungen Und Dibutadienylpiperazinverbindungen Von 2-Nitropentachlorbutadien

Nitrodiene compound 1 was stirred with allylthiol for a long time and compound 3 was obtained. Compound 1 gave bis(thio)substituted 2-nitrodiene compound 4 and tris(thio)substituted 2-nitrodiene compound 5 with 2 moles allylthiol in the presence of NaOH in ethanol. Mono(allylthio)substituted diene compound 3 gave dibutadienyl substituted piperazine compounds with piperazine 6 in CH 2 Cl 2 (or diethylether). Compound 3 gave compound 9 with compound 8 . Compounds 11a-e have been obtained from the reaction of compound 3 with compounds 10a-e . Nach langem Rühren von der Verbindung 1 mit Allylthiol entsteht die Verbindung 3 . Die Verbindung 1 liefert mit zwei Mol von Allylthiol in ethanolischer Natronlunge die bis(thio)substituierte 2-Nitrodienverbindung 4 und tris(thio)substituierte Dienverbindung 5 . Mono(allylthio)substituierte Dienverbindung 3 ergibt mit Piperazine in CH 2 Cl 2 (oder in Ether) die dibutadienylsubstituierte Piperazinverbindung 7 . Die Verbindung 3 liefert mit der Verbindung 8 die Verbindung 9 . Durch die Reaktion von der Verbindungen 10a-c wurden die Verbindungen 11a-e erhalten.     

Asymmetric Michael reaction of diethyl malonate with crotonaldehyde catalyzed by chiral aminocarboxylates,amino alcoholates,and amino phenolates

Alkali metal salts of substituted (S)-prolines, alkali metal alkoxides of (S)-prolinol, and Na salts of chiral substituted 2-amino-2"-hydroxy-1,1"-binaphthyls can catalyze the asymmetric Michael reaction of diethyl malonate with crotonaldehyde to give adducts in >90% yields with ee up to 40%. The influences of the catalyst structure, the nature of the alkali metal cation, temperature, the solvent, and salt additives on the reaction outcome were studied.     

Convergent, regiospecific synthesis of quinolines from o-aminophenylboronates

A direct convergent two-component synthesis of quinolines from alpha,beta-unsaturated ketones and o-aminophenylboronic acid derivatives is reported. The reaction is regiocomplementary to the traditional Skraup-Doebner-Von Miller synthesis and proceeds under basic rather than strongly acidic conditions. Quinolines substituted in the benzenoid ring can be accessed by using substituted o-aminophenylboronates prepared by direct palladium-catalyzed borylation of the corresponding o-bromoanilines.     

Enaminones as building blocks in organic synthesis: A novel route to polyfunctionally substituted benzonitriles,pyridines, eneylbenzotriazoles and diazepines

An efficient synthesis of enaminones 1a‐c is reported. Compounds 1a‐c reacted with diefhyl‐3‐amino‐2‐cyanopenten‐1,5‐dicarboxylate ( 3 ) to yield the benzonitriles 6 . On the other hand, the reaction of la‐c with 3‐amino‐2‐cyano‐2‐pentene dinitrile ( 7 ) afforded a mixture of benzonitriles 10 and pyridines 9 . The reaction of la‐c with 3‐aminocrotononitrile 11 has afforded the 4‐substituted‐3‐cyano‐2‐methylpyridines 15a‐c . The reaction of ethylene diamine with la‐c afforded 5‐substituted‐2,3‐dihydro‐lH‐[1,4]diazepines 18a‐c . On the other hand, la‐c reacted with o‐phenylenediamine to yield the 4‐(2‐aminopheynlamino)‐substituted enaminones 21 . Compounds 21 could be converted into the benzotriazolylenones 22 on treatment with sodium nitrite in acetic acid solution.     

Reactions between Grignard reagents and heterocyclic N-oxides: stereoselective synthesis of substituted pyridines, piperidines, and piperazines

In this perspective we discuss the recent developments of stereoselective synthesis of substituted pyridines, piperidines, and piperazines from cheap and commercially readily available starting materials. Pyridine N-oxides and pyrazine N-oxides are reacted with alkyl, aryl, alkynyl and vinyl Grignard reagents to give a diverse set of heterocycles in high yields. Optically active substituted piperazines are obtained by an asymmetric reaction from pyrazine N-oxides using sparteine as chiral ligand. In addition, a stereoselective synthesis of dienal-oximes from the reaction between pyridine N-oxides and Grignard reagents is presented, which results in a useful intermediate for the synthesis of a diverse set of compounds.     

Synthesis of New 1,3,4‐Oxadiazol,Thiadiazole, 1,2,4‐Triazole,and Arylidene Hydrazide Derivatives of 4‐Oxo‐1,4‐dihydroquinoline with Antimicrobial Evaluation

A series of substituted 1,3,4‐oxadiazole, 1,2,4‐triazole, and 1,3,4‐thiadiazole derivatives of the substituted 3‐carboethoxy‐1,4‐dihydro‐4‐oxoquinoline have been synthesized through the reaction of the key intermediate thiosemicarbazide derivatives with different reagents. N′‐Arylidene‐4‐oxo‐1,4‐dihydroquinoline‐3‐carbohydrazides were also synthesized through the condensation reaction of the corresponding hydrazides with the appropriate aldehydes. Antimicrobial activity of some of the synthesized compounds was evaluated.     

Copper Catalyzed Synthesis of Thiomorpholine Derivatives: A New Entry of Multicomponent Reaction Between Terminal Alkynes,Isothiocyanates, and Aziridines

Copper acetylide was reacted with isothiocyanate and aziridines to form 1,4‐thiomorpholine derivatives. Reaction outcome depends highly on the reaction conditions and the particular solvent employed. Optimum conditions are developed using copper iodide in hexafluoro‐2‐isopropanol at 60°C. Both the alkyl‐substituted and aryl‐substituted aziridines and terminal alkynes were studied.     

Photolytic reaction of chromium and molybdenum carbene complexes with imines : Synthesis of cepham, oxapenam, and oxacepham derivatives

A variety of substituted β-lactams, including a cepham analog, were synthesized by the photochemical reaction of [(methoxy)(methyl)carbene]chromium complexes with substituted imines. Oxazines and oxazolines were inert towards chromium carbene complexes. Oxazines were converted to bicyclic β-lactams by the photolytic reaction of molybdenum carbene complexes. Oxazolines were considerably less reactive and produced only low yields of β-lactam product and an equivalent amount of the corresponding oxazinone, incorporating two (MeO)(Me)C(CO) groups.     

1, 3-Cycloadditions to Highly Substituted,Strained Double Bonds: Spiro β-lactams from α-methylidene-β-lactams by reactions with diphenylnitrilimine,acetonitrile oxide,nitrones, and diazomethane

Substituted dihydropyrazole-spiro-β-lactams and isoxazolidine-spiro-β-lactam derivatives are regio- and stereoselectively prepared by 1, 3-cydoadditions between substituted α-methylidene-β-lactams and diazomethane, nitrones, or the in-situ-prepared dipoles ‘diphenylnitrilimine’ and acetonitrile oxide. These reactions represent examples for 1, 3-cycloadditions to the highly substituted, strained double bonds of α-methylidene-β-lactams, and they need special experimental conditions as all reaction products are relatively unstable. Especially in solution, the reverse reaction is highly favoured. Regioselectivity and stereoselectivity of the reactions are elucidated mainly by NMR techniques such as 2D-INEPT, ATP, and NOE experiments.     

A novel three-component reaction of allenoates, isocyanides, and carboxylic acids: facile synthesis of highly substituted acryl imide derivatives

A novel synthesis of highly substituted acryl imide derivatives by the three-component reaction of allenoates, isocyanides, and carboxylic acids was reported, and the intramolecular cyclization reaction of allenoic acids with isocyanides was also described.