Zincke exchange reactions

Amides can also be obtained by AICI3 catalyzed ester amine exchange which proceeds primarily without racemization of chiral centers (eq 24). The reaction of phenols with /3-keto esters is known as the Pechmann condensation (eq 25). Aryl amines are used in the Riehm quinoline synthesis (eq 26) Aromatic systems may be coupled via the Scholl reaction (eq 27) and indole derivatives are prepared in the Stolle synthesis (eq 28). In the Zincke-Suhl reaction, phenols are converted to dienones (eq 29). 3 ... 

The Zincke reaction is an overall amine exchange process that converts N- 2,A-dinitrophenyl)pyridinium salts (e.g, 1), known as Zincke salts, to iV-aryl or iV-alkyl pyridiniums 2 upon treatment with the appropriate aniline or alkyl amine. The Zincke salts are produced by reaction of pyridine or its derivatives with 2,4-dinitrochlorobenzene. This venerable reaction, first reported in 1904 and independently explored by Konig, proceeds via nucleophilic addition, ring opening, amine exchange, and electrocyclic reclosure, a sequence that also requires a series of proton transfers. By... 

With a chiral phenylglycinol nucleophile (Scheme 8.4.17), use of the chloride Zincke salt 6 (cf. Scheme 8.4.16) gave decomposition of the salt back to isoquinoline and 2,4-dinitrochlorobenzene. The desired reaction was enabled by exchanging chloride for the weakly nucleophilic dodecyl sulfate anion. The resulting salt 49 also had improved... 

The configuration of the amine was retained, except in the case of amino acid derivatives, which racemized at the stage of the pyridinium salt product. Control experiments showed that, while the starting amino acid was configurationally stable under the reaction conditions, the pyridinium salt readily underwent deuterium exchange at the rz-position in D2O. In another early example, optically active amino alcohol 73 and amino acetate 74 provided chiral 1,4-dihydronicotinamide precursors 75 and 76, respectively, upon reaction with Zincke salt 8 (Scheme 8.4.24). The 1,4-dihydro forms of 75 and 76 were used in studies on the asymmetric reduction of rz,>S-unsaturated iminium salts. 

The Zincke reaction is an overall amine exchange process that converts N- 2,A-dinitrophenyl)pyridinium salts, known as Zincke salts, to A -aryl or A -alkyl pyridiniums upon treatment with the appropriate aniline or alkyl amine. 

Examples of the Zincke reaction are ring-opening reactions of the pyridinium salt 54 (A = 2,4-dinitrophenyl) with aqueous alkali (leading to aminodienal 57 and to gluta-condialdehyde 58 by hydrolysis) and with aniline (leading to bisanil 59 after subsequent amine exchange) ... 

Knorr s. Konigs Koch-Haaf synthesis 14, 773 Kolbe electrolysis 23, 887 K5nig s. a. Zincke K5nigs-Knorr reaction 1, 218 modified 22, 228 23. 242 KU-1 cation exchanger 11, 232 suppl. 21 KU-2 cation exchanger 7, 730 suppl. 21 11, 232 suppl. 22 22,3... 

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