Nitrogen, heterocyclic compounds piperidine

Nonaromatic heterocyclic compounds piperidine for example are similar m basic ity to alkylamines When nitrogen is part of an aromatic ring however its basicity decreases markedly Pyridine for example resembles arylammes m being almost 1 mil lion times less basic than piperidine... 

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. 

In addition, silver-catalyzed asymmetric aza-Diels-Alder reactions provide a useful route to optically active nitrogen-heterocyclic compounds such as piperidines or pyrid-azines. Substituted dihydrobenzofurans can also be enantioselectively prepared through silver-promoted allylation of aldehydes. Other types of silver-mediated cyclizations can also be used in the synthesis of tetrahydrofnrans, tetrahydropyrans, 1,2-dioxetanes, 1,2-dioxolanes, medium-sized lactones, dihydroisoqninolines, and so on. Silver salts can also be used as cocatalysts with other transition metals. Unique activity was observed for these silver-based systems in several cases. Conseqnently, the use of silver can enrich several available heterocyclization methods, and fnrther developments in the application of chiral silver complexes will hopefnlly appear in the near future. 

Nonaromatic heterocyclic compounds, piperidine, for example, are similar in basicity to alkylamines. When nitrogen is part of an aromatic ring, however, its basicity decreases markedly. Pyridine, for example, resembles arylamines in being almost 1 million hmes less basic than piperidine. 

Nitrogen-containing heterocyclic compounds, including 1,2,3,4-tetrahydroqui-noline, piperidine, pyrrolidine and indoline, are also popular hydrogen donors for the reduction of aldehydes, alkenes, and alkynes [75, 76]. With piperidine as hydrogen donor, the highly reactive 1-piperidene intermediate undergoes trimer-ization or, in the presence of amines, an addition reaction [77]. Pyridine was not observed as a reaction product. 

PA (piperidine-2-carboxylic acid) is a nitrogen-containing heterocyclic compound with a molecular weight of 129.2. Its structure is shown in Fig. 2.4.1. 

In aliphatic heterocyclic compounds, the nitrogen atom is part of a saturated heterocyclic ring and the lone pair of electrons is available for reaction with protons (e.g. piperidine, Figure 3.19). Compounds of this type are similar in base strength to their open-chain aliphatic counterparts with typical pK3 values of 8-9. 

Heterocyclic compounds hold a special place among pharmaceutically significant natural products and synthetic compounds. The synthesis of nitrogen-containing heterocycles such as substituted azetidines, pyrrolidines, piperidines, azepanes, 2V-substituted 2,3-dihydro-1//-isoindoles, 4,5-dihydropyrazoles, pyrazolidines and 1,2-dihydrophthalazines has been accomplished in an aqueous medium under the influence of MWs (Scheme 8.15).2" ... 

Asymmetric aza-Diels-Alder reactions provide a useful route to optically active nitrogen-containing heterocyclic compounds such as piperidines, tetrahydroquino-lines, and so on. 

A large number of heterocyclic compounds of oxygen, nitrogen, and sulfur are prepared by condensation of di- or poly-functional compounds. Nitrogen-containing heterocycles by the thousands have been prepared by such reactions. The simplest such reaction is one leading to the preparation of a pyrrolidine or piperidine derivative. The synthesis of pyrrolidine may be accomplished by reaction of ammonia and 1,4-dichlorobutane in a stepwise process that may include an intramolecular displacement of chloride from the aminoalkyl chloride [Eq. (31)] or of ammonia from the aminoalkyl amine hydrochloride" [Eq. (32)] each process is known to occur. 

Three-membered Ring Nitrogen Heterocycles Four-membered Ring Nitrogen Heterocycles Pyrrolidines and Related Compounds Piperidines and Related Heterocycles... 

In organic chemistry, A -heterocyclic compounds are cyclic compounds containing one or more nitrogen atoms. A -Heterocyclic compounds include aromatic A -heterocycles such as pyrrole, pyridine, and imidazole, as well as saturated A -heterocycles such as aziridine, piperidine [1]. A -heterocyclic compounds are very important motifs in biochemical compounds such as nitrogenous bases, as well as pharmaceuticals and materials (Fig. 1.1). Significant synthetic efforts had been made toward A -heterocycles with different structures and substitutents [1] however, it is still demanding to develop new synthetic methods toward A -heterocyclic compounds, especially via metallacycles such as zirconacycles. 

Amines in which a nitrogen atom is part of a ring are common in biological systems. For example, pyrrohdine and piperidine are five- and six-membered heterocyclic compounds that are secondary amines. Pyridine is an aromatic amine considered a tertiary amine since there are three bonds to nitrogen. 

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