Nitropyridines, conversion

Laviron has studied an especially interesting class of nitro compounds containing a second basic site, e.g. 4-nitropyridine (14)33. Even two-dimensional representations such as those encountered earlier (Schemes 2-4) are inadequate to represent this mechanistically very complex situation. Laviron showed, however, that the electrochemical conversion of 14 to the corresponding ArN(OH)2 species can be satisfactorily explained in terms of a modified so-called bi-cubic diagram (Figure 1). Note that the each of the front and rear planes of the bi-cubic model consists of a seven-component reaction diagram analogous to that of... 

Most nitrations of pyridines take place on the A-protonated species, and this includes the conversion of 2,6-dimethoxypyridine to the 3-nitro derivative. However, the further nitration of 2,6-dimethoxy-3-nitropyridine to the 3,5-dinitro derivative occurs on the free base. The introduction of the first nitro group reduces the basicity such that sufficient free base is now present for the reaction to take place through this minority species. 2,6-Dihalopyridines also undergo nitration as free base. 

Conversion of 2-hydroxypyridines to 2-chloropyridines has been effected using triphenylphosphine and NCS <1999TL7477, 2001HCA1112>. Interestingly, 5-nitropyridine-2-sulfonic acid is converted to 2-chloro-5-nitropyr-idine in 87% yield when treated with phosphorus pentachloride (Equation 41). This reaction provides a new pathway to chloronitropyridines <20030BC2710>. 

Just as in benzene chemistry, all types of halogen atom are activated toward nucleophilic displacement by the presence of other electron-withdrawing substituents. This is illustrated by the conversion of 2-chloro-5-nitropyridine 938 to the 2-hydrazine derivative (N2H4, 20 C) or the 2-thione 939 under relatively mild conditions. 

Nitropyridines with a suitable N-C-C substituent in the 2-position will, after the conversion of the nitro substituent into a function containing an N-H group, cyclize to give pyrido[2,3-Ajpyrazines. 

An interesting ort/io-aminophenylation reaction of reactive heterocycles is exemplified by the conversion of 4-chloro-3-nitropyridine (39) into the o-aminophenyOpyridone (40). The ortho-ortho-lmked product contrasts with the previously discovered reaction of 2-chloro-3-nitropyridine, which, under the same conditions, gives a para-para- inked product. This very rare ortho-ortho benzidine-type rearrangement only occurs when a para-position is blocked, and has also been carried out with appropriately substituted pyrimidine and benzene derivatives (Scheme 18). 

In this paper we report phase-matched second-harmonic generation in nonlinear optically active Langmuir-Blodgett (LB) film waveguides both by mode conversion and by use of the Cerenkov-type configuration. The experiments were done in 2-docosylamino-S-nitropyridine (DCANP) LB films (Hg.l). The synthesis, the optimum conditions for LB film transfer and the linear and nonlinear optical properties of this material have been described elsewhere [4-6]. 

Sulphenyl and Selenenyl Halides.—The preparation of these compounds by halogenolysis of disulphides and diselenides, a particular example being the preparation of the stable 3-nitropyridine-2-sulphenyl chloride and bromide, has not proved suitable for sulphenyl fluorides. Evidence for the existence of PhSF as an intermediate in the conversion of diphenyl disulphide into thianthrene has been provided by F n.m.r. studies. Addition of SClj to alkenes is rarely used, since... 

Copper(I)-catalyzed amination of iodobenzene with aniline in the presence of KO-t-Bu as base was described by Don and co-workers [56] (Scheme 22.12). They reported the use of the [Cu2(p-I)2(L)2] (L = l,2-bis(diphenylphosphino)-c/oi 0-carborane(12) (1)) catalyst, which showed a conversion of the amine of 58%, compared to no significant conversion without ligand 1. The conversion is in the range of the reaction of copper(I) iodide in the presence of 2,2 -dithiobis(5-nitropyridine) but lower than that of the 2,2 -bipyridine ligand [57]. It was postulated that the reaction proceeds via an insertion of the copper(I) species into the carbon-halogen bond as the initial step. 

Examples are known of the conversion of 2-nitropyridines into 2-halogeno-pyridines by reaction with halogen hydracids 185, 240, 847 Thus, 3-ethoxy-2-nitropyridine with hydrobromic in acetic acid gives 2-bromo-3-ethoxy- or 2-bromo-3-hydroxy-pyridine, according to conditions, whilst... 

Nitramino- or acetic acid-acetic anhydride i 222 nd by heating 2-nitramino-5- nitropyridine with sulphuric acid some workers22i obtained 2-hydroxy-5-nitropyridine rather than 2-amino-3,5-dinitropyridine (p. 172). The mechanism of the conversion of nitramines into pyridones by acid is unknown. 2-Nitramino-5-nitropyridine also gives 2-hydroxy-5-nitropyridine and nitrous oxide quantitatively with warm dilute alkali22i. 

Alkaline cleavages are rare. 3-Ethoxy-6-nitropyridine is very sensitive to alkali , but the result of the reaction is obscured by decomposition. What is happening in the conversion of 5-methoxy-l,2-dimethyl-4-pyridone into 5-hydroxy-l,2-dimethylpyrid-4-one by sodium and amyl alcohol i is not clear. 

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