Pyridones structures

A positively charged heteroatom can be balanced by a negatively charged substituent, and if they are oriented favourably relative to each other the charges may formally cancel. Thus, the 2- and 4-pyridone structures (26, 27 X = NH) and the corresponding pyrones... 

The availability of functionalized 2(lH)-pyrazinone in combination with the use of microwave accelerated solid-phase chemistry constitutes a sohd foundation for generating large libraries of compoimds suitable for medicinal chemistry. The authors have also shown that the scaffold can be further functionalized using the principles of cUck-chemistry , thereby paving the way towards highly substituted 2-pyridone structures [45-47]. 

Ring-fused 2-pyridone structures where the additional ring is fused over the nitrogen will be covered in this section. Other ring-fused systems can be obtained simply by using suitable cychc starting materials or by conducting intramolecular reactions, examples for the preparation of such systems can be found in the papers discussed in Sect. 2.2 [42,43]. 

Coleman and Sivy also used an infrared transmission cell to undertake degradation studies under reduced pressure on a series of poly(acrylonitrile) (ACN) copolymers [30-33]. Thin films prepared from a polymer were mounted in the specially designed temperature-controlled cell mounted within the infrared spectrometer. The comparative studies were made on ACN copolymers containing vinyl acetate [30,32], methacrylic acid [30,31] and acrylamide [30,33]. The species monitored was the production of the cyclised pyridone structure. This was characterised in part by loss of C=N stretch (vC = N) intensity at 2,240 cm-1 accompanied by the appearance and increase in intensity of a doublet at 1,610/1,580 cm-1. 

Vinyl isocyanates, readily available from the corresponding a,/3-unsaturated acids by a Curtius procedure, have been by far the systems studied in more detail, mainly by the Rigby group, e.g., in the construction of the pyridone ring (Scheme 53). Thus, heteropolycyclic compounds having 2-pyridone structure 233 were shown to be formed in moderate to... 

A different pathway was elucidated for the oxidation of 70. Predominantly, the oxidative elimination of 2-alkyl substituents occurs simultaneously with the formation of the pyridone structure, with 71 being the major oxidation product of 70. Compound 73 is only of minor importance as an intermediate, since it is oxidized itself to a large extent to 72 by ferricyanide (Scheme 15). A... 

Nicotinic acid undoubtedly provides the basic skeleton for some other alkaloids. Ricinine (Figure 6.35) is a 2-pyridone structure and contains a nitrile grouping, probably formed by dehydration of a nicotinamide derivative. This alkaloid is a toxic constituent of castor oil seeds (Ricinus communis Euphorbiaceae), though the toxicity of the seeds results mainly from the polypeptide ricin (see page 434). Arecoline (Figure 6.36) is found in Betel nuts (Areca catechu Palmae/Arecaceae) and is a tetrahydronicotinic acid derivative. Betel nuts are chewed in India and Asia for the stimulant effect of arecoline. 

In a-hydroxypyridine (Fig. 3), which exists mainly in the pyridone structure, the elimination of CO is the predominating cleavage re-... 

Trimesic acid 5-Methyl-2-pyridone Structure of a new cocrystal product generated by solid-state grinding of the methanol solvate cocrystal [52]... 

Although the pyridone structure had been deduced previously from conventional IR spectra by several authors, the reaction path is new, and appears to be plausible. The suggested mesomerism is based on the known fact that such mesomerism exists in tetrahydropyridine, which has an analogue structure ... 

The differentiation between 48 and 42 by spectroscopical means is not obvious but the X-rays of the crystalline product derived from ethyl acrylate upon oxidation to pyridone have unambiguously established its a-pyridone structure 5Q (Scheme 54). 

Biniak and co-workers reported that nitric acid treatment of carbon materials results in the formation of pyridine structures and pyridine-N-oxide species at the expense of pyrrolitic moieties [105]. An increase in the intensity of the bands at 1330 and 880 cm respectively, characteristic of pyridine, pyridine-N-oxide, or pyridone structures suggested that the ammonia treatment incorporated nitrogen into the carbon aromatic lattice with the formation of pyridinelike structures. The assigmnent of other nitrogen-containing bonds that can be found on the carbon surface is presented in Table 2.4. 

Similar properties are found with the oxo function at the 4-position the y-pyridone structure is greatly favored over the hydroxyl form, with resonance as shown in Scheme 6.34. The 2,3-double bond transmits the electron-releasing effect of the NH group to the C=0 group the stmctural unit is known as a vinylogous or pseudo amide, and it has the reactivity of an amide. Thus, with PCI5, a y-pyridone is converted to a 4-chloro pyridine. 

CijHjoNjOj. Mr 260.34, mp. 210 C, (aJc -147.7° (C2H5OH). Tetracyclic quinolizidine alkaloid of the sparteine type with an a-pyridone structure from several genera of the Fabaceae (e. g., Baptisia, Caulophyl-lum, Sophora). In analogy to 13-hydroxylupanine, esters of B. occasionally occur, and generally as the acetates. The 13-epimer epi-baptifoline (mp. 215 C, [o]d 138.9°) is often found together with B. . 

The infrared spectra of 2- and 4-pyridones are consistent with the pyridone structure. A comparison of the infrared spectra of 2-pyridone and 2-pyridone- 0 indicates that the lactam description is better than the dipolar one. A comparison of infrared and Raman spectra of 4-pyridone (XIM70, R = H) with those of 4-pyridinium ions and a rationalization of the dipole moment has led to the estimate that the upper limit of the contribution to 4-pyridone by the dipolar form (XII470b, R = H) is lOto 15%. ... 

The NMR spectrum of 4-pyridone in aqueous solution is consistent with a pyridone structure. In deuterochloroform, the NMR spectra of 2- and 4-pyridone- N show a very rapid intermolecular exchange of the enolizable proton. The observed N-H coupling of 90 Hz at low temperature indicates that the relative amount of the 2-pyridinol tautomer is less than A study of "nitrogen-hydrogencoupling in 4-pyridone was thwarted by its poor solubility at lower temperatures. ... 

The dimethyl and diethyl esters of 2,6-di-a-pyridinyl- and 2,6-di-a-quinolinyl-4-hydroxy-3,5-pyridinedicarboxylic acids (XH-479)also exist in the solid state a conjugate chelates. 2,6-Diphenyl-4-pyridone, which does not possess the ortho-hydwxy ester structural feature of XEI-479, exists as the pyridone (XII-480) in the solid state and in solution. 3-Acetyl-4,6-dimethyl-2-pyridone (W-481) exists as the pyridone tautomer in methanol. Stabilization of the pyridinol form by hydrogen bonding does not occur. The infrared (KBr) and ultraviolet spectra (ethanol) of 3-hydroxy-2-pyridone are consistent with the pyridone structure (XII-482). ... 

The 4-hydroxy-6-methyl-2-pyridone structure (XII-483) is consistent with its NMR, ir, and uv spectra and is similar to that of 4-hydroxy-2-pyridone. Ultraviolet spectra in water and ethanol and infrared spectra (KBr) show that glutazine and several of its derivatives (XII484 R = H,CN, CONH, C02Et) exist as an equilibrium mixture of the 4-amino-6-hydroxy-2-pyridone (XII-484a) and the 4-aniino-2,6-pyridinedione (XII-484b). ... 

Pyridone reacts with dibutyl dimethyloxytin to form dibutyldi-(2-pyri-donato-l)tin (XII-796), with dimethyl dichlorosilaneto form dimethyldi-(2-pyri-dinato-l)silane (XII-797), and with aluminum ethoxide to form tri-(2-pyri-dinato-l)aluminum (XII-798). Infrared spectra are consistent with an A -substi-tuted pyridone structure. ... 

The alkaloid piplaitine XII-834, isolated from the roots of Piper hngum I. inn., is identical with piperlongumine. A 3,4-dihydro-2-pyridone structure was first proposed, but a detailed NMR study has shown it to be/V-[ 3,4,5-tri-methoxyphenyl)acrylyl]-5,6-dihydro-2 )yridone (XlI-834) Blastidone... 

XANES has been shown to be a very useful techuique for the identification of nitrogen, sulfur, and oxygen functional groups iu carbonaceous materials [130], It allows, in particular, the distinctiou between pyrroUc and pyridonic structures, which is impossible to make by XPS. However, it does suffer from difficulties in the quantification of the species present, and it is of course less accessible and more costly [126] as it needs a synchrotron. It must be kept in mind that although XPS permits analysis of the sample surface only, XANES allows analysis of the bulk of a sample. 

---