Of nitrogen-containing heterocycles

Dimethyl acetylenedicarboxylate gave first a similar adduct (2) which then added further molecules of furan yielding (3) and subsequently (4). Between 1931 and 1940 the reactions of acetylenedi-carboxylic acid and its dimethyl ester with a number of nitrogen containing heterocyclic compounds were examined, and structures were proposed for the products. Apart from an unpublished investigation of the products from pyridine and dimethyl acetylenedicar-... 

Reversible covalent hydration across C=N bonds occurs in a number of nitrogen-containing heterocycles, including pteridine and its 2- and 6-hydroxy derivatives, quinazoline (as the cation), and 1,4,6-triazanaphthalene (as the cation). Among bases giving this reaction, the neutral molecule exists predominantly as the anhydrous form, whereas the cation contains an increased proportion of the... 

The reversible hydration of nitrogen-containing heterocyclic bases and their hydroxy and mercapto derivatives is acid-base catalyzed and, at constant pH, the reactions obey first-order rate equations. 2 26.27-33... 

O. V. Kharitonova, A. B. Sheremetev, andT. S. Novikova, in The Vth All-Union Conference on Chemistry of Nitrogen Containing Heterocyclic Compounds., Oetober 22-25, 1991, Chernogolovka, USSR, 227 (in Russian). 

Other thietane derivatives have been obtained by isomerization of nitrogen-containing heterocycles. The reaction of an acyl isothiocyanate (RCONCS) with diphenyldiazomethane gave 20 and this isomerized in solution to the tetraphenyl-3-thietanone 21 <96BSB253>. Additionally, the isoxazolidine 22 was converted into 23 by the action of trimethylsilyl iodide and zinc iodide <96H1211>. 

This method is the basis for synthesis of nitrogen-containing heterocyclic compounds when Z is a carbonyl-containing substituent.290... 

HMBC experiments are not limited to proton-carbon interaction. With suitable hardware, it is possible to acquire 1H-I5N spectra which can be extremely useful for confirming the identity of nitrogen-containing heterocyclic compounds. The sensitivity of this technique is very low, probably only about... 

Bowman and coworkers described another nice approach in this field combining one anionic and two radical cyclization steps (Scheme 2.160) [368], Thus, they were able to construct differenttypes of nitrogen-containing heterocycles such as annulated pyrrolidines 2-724 and spiropyrrolidines 2-726 as well as indolizidines as 2-729. 

Reports of [ 2 + 2] cycloaddition of nitrogen containing heterocycles to alkenes are so numerous that attention can be drawn here to only a few. Recent examples include the acetone-sensitized photoaddition of 4-oxazolin-2-one (248) to ethylene to give the cis-adduct 249,203 the photocycloadditions of N-substituted imidazoles to acrylonitrile204 and of N-methyl-4-hydroxy-quinol-2-one to cyclohexene,205 and the photoaddition of pentafluoro-pyridine to ethylene to give the 1 1- and 1 2-adducts 250 and 251,... 

The synthesis of nitrogen containing heterocyclic systems by photocylo-addition processes is virtually limited to examples involving [ 2 + 2] cycloaddition of imines, nitriles, and azo compounds. Successful additions are few in number and the requirements for success uncertain. The reactions do not proceed with the facility with which carbonyl containing compounds undergo photocycloaddition to alkenes to give oxetans, and various explanations have been advanced to account for this observed lack of reactivity.226... 

Molecules containing the imino function are commonly reduced to hydro-dimeric products when irradiated in isopropyl alcohol, as illustrated in (4.1) 401 and (4.2) 402). The photoreduction of nitrogen containing heterocycles has been reviewed recently 403). 

Various schemes have been proposed to explain the production of nitrogen-containing heterocyclic compounds, such as pyrrolidines and piperidines, from proline. Nitrogen heterocyclic compounds are often potent flavouring chemicals. 

The influence of catalytic C,C-coupling of six-membered cyclic nitronates can be used, under more drastic conditions, for the constmction of nitrogen-containing heterocycles via cascade chemical transformations (see, e.g., the coupling reaction of nitronate (368) with silyl enolates (369a-d) in the presence of trimethylsilyl triflate (154) (Scheme 3.211)). 

Additional data on the use of oxazine (539) and products of its modifications in syntheses of compounds having potential biological activity and their precursors are presented in Scheme 3.274 (541). Catalytic hydrogenation of the imino and oximino fragments is primarily used for this purpose. This approach made it possible to prepare a representative series of nitrogen-containing heterocycles and of other previously unknown compounds. 

SN NMR spectroscopy is still underexploited in structural analysis of nitrogen-containing heterocycles. It can however be a powerful tool, for instance in tautomerism studies <2002JP2126>. Some 1SN NMR investigations of lanthanide induced shift have been performed on bicycles 50-52, showing that the complexing site of these 4,5-dihydro-l/f-l,2,3-triazoles is located on N-3. 

AO is also effective in metabolizing a wide range of nitrogen-containing heterocycles such as purines, pyrimidines, pteridines, quinolines, and diazanaphthalenes (95). For example, phthalazine is rapidly converted to 1-phthalazinone by AO and the prodrug, 5-ethynyl-2-(l//)-pyrimidone, is oxidized to the dihydropyrimidine dehydrogenase mechanism-based inhibitor, 5-ethynyluracil, by AO (Fig. 4.40) (96). 

Table 3.19 lists examples of the preparation of nitrogen-containing heterocycles by RCM. As mentioned in Section 3.2.5.3, free amines can partly deactivate metathesis catalysts. With the highly reactive molybdenum catalyst 1 it is, however, possible to cyclize dienes containing a basic amino group. If the less reactive catalysts 2 or 3 are to be used, protonation or acylation of the amine can be used to reduce their nucleophilicity. This will generally lead to higher yields with smaller amounts of catalyst. 

Table 3.19. Formation of nitrogen-containing heterocycles by ring-closing metathesis.

Table 4.11. Preparation of nitrogen-containing heterocycles by intramolecular N-H insertion of electrophilic carbene complexes.

Covalent Hydration of Nitrogen-Containing Heterocycles and Heterocyclic Pseudobases... 

The aza-Diels-Alder reaction is an important and versatile tool for the preparation of nitrogen-containing heterocycles present in numerous natural products and drug candidates. It involves the [4 + 2] cycloaddition of either an imine with an electron-rich diene or an azabutadiene with an electron-rich alkene (inverse electron demand). Catalytic asymmetric variants employing not only metal complexes, but also organic molecules were disclosed over the last few years. 

Muravyova EA, Chebanov VA, Shishkina SV, Musatov VI, Desenko SM (2009) An influence of temperature and activations regime on the multicomponent heterocyclizations of some aminoazoles. 5th international conference chemistry of nitrogen containing heterocycles , Kharkiv, Ukraine, 104... 

Some examples of nitrogen-containing heterocyclic compounds. 

Some examples of nitrogen-containing heterocyclic compounds containing more than one nitrogen atom. 

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