Pyridine hydrochloride 1.2.4- triazines

In this solvent the reaction is catalyzed by small amounts of trimethyl-amine and especially pyridine (cf. 9). The same effect occurs in the reaction of iV -methylaniline with 2-iV -methylanilino-4,6-dichloro-s-triazine. In benzene solution, the amine hydrochloride is so insoluble that the reaction could be followed by recovery. of the salt. However, this precluded study mider Bitter and Zollinger s conditions of catalysis by strong mineral acids in the sense of Banks (acid-base pre-equilibrium in solution). Instead, a new catalytic effect was revealed when the influence of organic acids was tested. This was assumed to depend on the bifunctional character of these catalysts, which act as both a proton donor and an acceptor in the transition state. In striking agreement with this conclusion, a-pyridone is very reactive and o-nitrophenol is not. Furthermore, since neither y-pyridone nor -nitrophenol are active, the structure of the catalyst must meet the conformational requirements for a cyclic transition state. Probably a concerted process involving structure 10 in the rate-determining step... 

Triazines on reaction with enamines followed by loss of a nitrogen from the intermediates give pyridine derivatives (85H2789) (Scheme 56). The reaction of 1,3,5-triazine with enamine and enaminoester hydrochlorides in acetonitrile leads to mixtures containing pyrimidines and pyridines... 

In some cases, the reaction of 1,3,5-triazine (1) with compounds containing a second acidic C —H group gives pyridines 9 or 10 in moderate yield. One example of this exception is the conversion of 2-cyanoacetimidate hyrochloride. Although all other related imidate hydrochlorides lead to pyrimidines, the product in this instance is a pyridine derivative.18,25... 

When 1,3,5-triazine (la) is treated with the hydrochlorides of N-unsubstituted enaminones 6, a mixture of the related pyrimidine 7 and a pyridine derivative 8 is formed. The reactions are carried out in refluxing acetonitrile for 6 h. The assumed reaction mechanism has been confirmed by 15N-labelling experiments.5... 

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