Nitrogen-containing piperidines pyridines

Tetrahydrofurfuryl alcohol reacts with ammonia to give a variety of nitrogen containing compounds depending on the conditions employed. Over a barium hydroxide-promoted skeletal nickel—aluminum catalyst, 2-tetrahydrofurfur5iarnine [4795-29-3] is produced (113—115). With paHadium on alumina catalyst in the vapor phase (250—300°C), pyridine [110-86-1] is the principal product (116—117) pyridine also is formed using Zn and Cr based catalysts (118,119). At low pressure and 200°C over a reduced nickel catalyst, piperidine is obtained in good yield (120,121). 

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. 

The basicity of heterocyclic amines varies over a wide range and reflects both the hybridization of the orbital of nitrogen containing the lone pair electrons and the effects of delocalization. Pyridine is a substantially weaker base than alkylamines such as piperidine. The electron pair of pyridine occupies an sp2-hybridized orbital and lies closer to the nucleus than the electron pair in the sp -hybridized orbital of alkylamines. As a result, pyridine is a weaker base (larger than an alkylamine. 

Pyridine and Piperidine. These are six-membered heterocyclic rings containing one nitrogen. Piperidine (azine) is aromatic and undergoes aromatic hydroxylation. Piperidine functions as a secondary amine and undergoes hydroxylation with either glucuronic acid or sulfuric acid. 

Any ring system containing at least one heteroatom (i.e. an atom other than carbon - typically nitrogen, oxygen, or sulphur) can be described as heterocyclic. This broad definition encompasses both aromatic heterocycles (such as pyridine 5.1) and their non-aromatic counterparts (piperidine 1.7). 

The hybridization of the orbital that contains an amine s lone pair also affects its basicity. This is illustrated by comparing the basicity of piperidine and pyridine, two nitrogen heterocycles. The lone pair in piperidine resides in an sp hybrid orbital that has 25% s-character. The lone pair in pyridine resides in an sp hybrid orbital that has 33% s-character. 

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. 

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