N-Aminoazonium salts

Tamura, Y., Ikeda, M., Advances in the Chemistry of Heteroaromatic N-Imines and N-Aminoazonium Salts, 29, 71. 

Heteroaromatic N-imines and N-aminoazonium salts 82AHC(29)71. Hetarylcarboranes 83KGS579. 

The N -unsubstituted N-imines are usually generated in situ by treatment of the N-aminoazonium salts with base and used directly for subsequent reactions because of the instability of the N-imines (Eq. 1). Some N-imines such as quinoline, isoquinoline, and phenanthridine N-imines are known to form crystalline dimers,17 which are in equilibrium with the N-imines in solutions.29 The only exception is benzo[c]cinnoline N-imine which is isolable as a stable crystalline solid.44... 

The N -substituted N-imines can be prepared by the reaction of the N-aminoazonium salts, in the presence or absence of base, with anhydrides or acyl halides,8,13-17,20,21,45,46 diketene,47 diethyl malonate,48 sulfonyl chloride,8,15,49,50 /i-halovinyl ketones and esters,51-54 diethyl ethoxymeth-ylenemalonate and related compounds,53,55-57 isocyanates,17,58 thioiso-cyanates,17,58 imidoyl chlorides and imidates,59,60 nitro acetate,8,61 and active halobenzenes.62,63 Some representative pyridine -(substituted imines) prepared in this way are shown in Scheme 1. 

Pyrylium salts also react with hydrazine and its derivatives to give the N-aminoazonium salts (Eq. 3), although the reaction takes other courses in some cases.50,70,80-93 The reaction involves the formation of intermediate hydrazones by nucleophilic attack at the a-position of pyrylium rings. The hydrazones undergo ring closure followed by dehydration. This method has been utilized for the preparation of highly substituted pyridine AT-imines. 

The reaction of N-aminoazonium salts with aliphatic and aromatic aldehydes in the absence of base gives the Schiff base type compounds 28.151,153-156 Some aliphatic ketones also react with N-aminoazonium salts.40,155 Hexane-2,5-dione reacts with N-aminopyridinium perchlorate to give l-(l -pyrrolyl)pyridinium cation 29 together with some of the bisper-chlorate 30.157 Certain esters such as diethyl malonate and ethyl cyano-acetate react with N-aminopyridinium salts in the presence of base to give the corresponding N-acylimines 31.48 However, the reaction of ethyl aceto-acetate and acetylacetone with N-aminoazonium salts in the presence of base gives 1,3-dipolar cycloaddition products (Section IV,C,1).36,154,158 The reaction of ethyl acetoacetate with 1-alkyl-l,2,4-triazole 4-imine affords zwitterionic triazolo[4,3-/>]pyridazines 32.139,159... 

Volume 29 consists of six contributions. Three of these deal with specific groups of compounds and update previous contributions in this publication on the same type of compounds. Thus, R. K. Smalley, who writes on The Chemistry of Indoxazenes and Anthranils 1966-1979, updates the article by Wunsch and Boulton published in 1967 in Volume 8. Raymond Bonnett and Stephanie A. North, writing on The Chemistry of the Isoindoles, update the contribution by White and Mann, published in Volume 10, in 1969, and Richard M. Scrowston, with his review entitled, Recent Advances in the Chemistry of Benzo[fe]-thiophenes, updates that by himself and Iddon in Volume II, published in 1970. The chemistry of Furoxans and Benzofuroxans is covered by A. Gasco and A. J. Boulton. This and the subject of Mononuclear Heterocyclic Rearrangements reviewed by Michele Ruccia, Nicolb Vivona, and Domenico Spinelli, are both topics close to the hearts of the Editors of this volume. Finally, Yasumitsu Tamura and Masazumi Ikeda have summarized Advances in the Chemistry of Heteroaromatic N-Imines and N-Aminoazonium Salts. Although this subject was reviewed as recently as 1974, in Volume 17 of Advances, its growth since then has been so dramatic that this further review is very timely. 

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