Pseudo-bases heterocycles

Pseudo bases, heterocyclic, 1, 167 Purine bases, aza analogs of, I, 189 Purines, physicochemical aspects of, 6, 1 Pyrazole chemistry, progress in, 6, 347 Pyridazines, 9, 211... 

The study of structure and reactivity of tertiary heterocyclic enamines is associated with the problem of equilibrium of the cyclic enamine form (70) and the tautomeric hydration products 173,174) quaternary hydroxide (71), pseudo base (so-called carbinolamine) (72) and an opened form of amino aldehyde or amino ketone (73). 

Hantzsch 2 gave the name pseudo bases to those carbinols that gave salts with acids by the elimination of water and a simultaneous change of constitution. Such carbinols are common among the nitrogen heterocyclic compounds and the naturally occurring alkaloids e.g., berberine, sanguinarine, chelerythrine. 

Thus the following problems are unsolved (1) Does the threefold tautomerism assumed by Gadamer really exist for heterocyclic pseudo bases and which factors determine the stability of the various forms (2) Does ring-chain tautomerism occur in the derivatives of these bases when this is formally possible, and if not, do these derivatives possess the cyclic or open-chain structure, and by what path have they been formed ... 

Thus among the known pseudo bases derived from heterocyclic quaternary ammonium salts, the following principal types can be differentiated according to their basicity ... 

The heterocyclic pseudobasic carbinolamines show a very varied reactivity. However, the structure of a large number of their transformation products, in particular those from which conclusions have been drawn as to the structure of the initial pseudo base, are incorrect even in the most recent literature. 

As an over-all conclusion, it can be stated that the assumption of ring-chain tautomerism in the pseudo bases derived from the heterocyclic quaternary ammonium salts is quite unnecessary as an explanation of the formation of two (cyclic and open-chain) types of deriva-... 

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