Iminium salts, heterocyclic, oxidation

The reduction of iminium salts can be achieved by a variety of methods. Some of the methods have been studied primarily on quaternary salts of aromatic bases, but the results can be extrapolated to simple iminium salts in most cases. The reagents available for reduction of iminium salts are sodium amalgam (52), sodium hydrosulfite (5i), potassium borohydride (54,55), sodium borohydride (56,57), lithium aluminum hydride (5 ), formic acid (59-63), H, and platinum oxide (47). The scope and mechanism of reduction of nitrogen heterocycles with complex metal hydrides has been recently reviewed (5,64), and will be presented here only briefly. 

V-Phenylbenzylimines undergo stilbene-type photocyclizations (equation 83) to yield heterocyclic compounds143. The reactions usually take place via the iminium salt and need oxidants like oxygen or iodine. Six-electron electrocyclic reactions have been observed for 1-aza-l,3-dienes144 (equation 84). 

A group of Italian workers from Modena, led by Professor Taddei, has reviewed published work on the conformations of acyl groups in heterocyclic compounds, including both C-acyl and N-acyl derivatives. The first recent review of the basicity and acidity of azoles, covering both gas-phase and solution measurements, is presented by a group of Spanish workers (Catalan et al.). H. Weber has summarized the considerable recent progress in oxidative transformations of heteroaromatic iminium salts. 

Heterocyclic iminium salts, oxidative transformation, 41, 275 Heterocyclic mesomeric betaines and analogs in natural product chemistry, 85, 67 Heterocyclic oligomers, 15, 1 Heterocyclic products, natural, synthesis of by hetero Diels-Alder cycloaddition reactions, 42, 245... 

Iminium salts, oxidative transformation of heterocyclic, 41, 275 Indole Grignard reagents, 10, 43 Indole(s)... 

Imidazoles, 35, 375 4f/-Imidazoles, 35, 413 Imidazolium azolate inner salts, 60, 197 At-lmines, heteroaromatic, 17, 213 29, 71 Iminium salts, oxidative transformation of heterocyclic, 41, 275 Indole Grignard reagents, 10, 43 Indole(s)... 

Photochemistry of heterocyclic iminium salts 83ACR130, 83T3845. Photochemistry of heterocyclic N-oxides 84CRV43. 

Isoquinolones. When N-methylisoquinolinium iodide (1) in f-butyl alcohol is treated with solid KOH and then oxygenated, N-methylisoquinolone (2) is obtained in 827o yield. The oxidation is believed to involve the pseudo base a. The choice of solvent is important, but the substituent on nitrogen does not affect the yield. Also, the reaction appears to be general for heterocyclic iminium salts. ... 

If one keeps in mind that this process can provide N-oxides of polysubstituted heterocyclic compounds from simple olefins, further improvement of face selectivity would certainly be welcome, one of the reasons being that the N-oxides obtained this way, as well as those prepared by peracid oxidation, have proven to be broadly applicable precursors of iminium salts and enamines, which are both of high value in alkaloid synthesis. 

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