Imine exchange

Formamidine-urea compounds (45) exchange imine fragments with primary amines (R4NH2) in non-protic solvents via the breakdown of the tetrahedral intermediate... 

Deuteration of C-methyl protons in simple methylpyrimidines and their amino and hydroxy derivatives has been studied under acidic and basic conditions. The exchange is acid/base catalyzed with, for example, a minimal rate at pH 4 for 1,4,6-trimethylpyrimidin-2(lH)-imine (67JCS(B)171). 

Pyridin-4-one, 1 -hydroxy-2,6-dimethyl-hydrogen-deuterium exchange reactions, 2, 196 Pyridin-4-one, 1-methyl-hydrogen-deuterium exchange, 2, 287 pK 2, 150 Pyridin-2-one imine tautomerism, 2, 158 Pyridin-2-one imine, 1-methyl-quaternization, 4, 503 Pyridin-4-one imine tautomerism, 2, 158 Pyridinone methides, 2, 331 tautomerism, 2, 158 Pyridinones acylation, 2, 352 alkylation, 2, 349 aromaticity, 2, 148 association... 

The formation of bicyclic imines (263,264) from piperidine enamines and y-bromopropyl amines may appear at first sight to be a simple extension of the reactions of enamines with alkyl halides. However, evidence has been found that the products are formed by an initial enamine exchange, followed by an intramolecular enamine alkylation. Thus y-bromodiethylamino-propane does not react with piperidinocyclohexene under conditions suitable for the corresponding primary amine. Furthermore, the enamine of cyclopentanone, but not that of cyclohexanone, requires a secondary rather than primary y-bromopropylamine, presumably because of the less favorable imine to enamine conversion in this instance. 

The imine is exchanged away with Girard reagent T to give... 

The suggested reaction mechanism involves a nucleophilic attack of the imine nitrogen at the activated triple bond, followed by a proton exchange, to give a benzimidazolinium system which, by intramolecular attack at the carbonyl group, leads to an epoxide that ring opens to the observed product. For the ethyl derivative (R = Et) a tub conformation could be established by X-ray crystallographic analysis.33... 

Phosphorous acid has also been of use for additions to imines. Originally investigated by Moedritzer and Irani,241 who developed a Mannich-type procedure for the preparation of phosphorus-centered species, the approach was found later to be useful for both primary and secondary amines in reaction with formaldehyde and phosphorous acid. The approach was later used for the preparation of a cationic exchange resin using a polymer substrate.242... 

Scheme 22 summarizes the mechanism proposed. As in the case of oxygen exchange between MeRe03 and H20, the proposed intermediate was not detected. Examples of analogous intermediates that carry out the hydrolysis of imines and the aminolysis of ketones are well documented (64-66). 

A fundamentally different approach to the synthesis of 3-pyrrolines is evidenced in the annulation in Eq. 13.50 [58]. Ethyl 2,3-butadienoate 150 reacts with N-sulfony-limine 151 in the presence of triphenylphosphine under very mild conditions to give JV-protected 3-pyrroline 152 in 90% yield. The mechanism that has been postulated is related to that of the Baylis-Hillman reaction. Michael addition of triphenylphosphine to the allenyl ester generates a zwitterion that combines with the imine to give 153 in a non-concerted process. This is followed by ring closure, proton exchange and expulsion of triphenylphosphine to give 152. This annulation is successful only for aromatic or cinnamyl imines [59]. 

Fig. 6.4 Reversible interconversion of amino acid and keto acid. Conjugation of the imine bond in the aldimine with the electron sink of the pyridine ring plus protonation of the pyridine nitrogen as well as the metal ion - all this results in weakening of the C-H bond of the amino acid residue. Thus, also catalyzed is a-proton exchange, racemization of a chiral center at the a-carbon atom and decarboxylation of the appropriate amino acid. ...

Amberlyst 15 DRY, a sulfonic cation exchange resin with a large surface area, was found to catalyze the imino aldol reaction of imines with ketene silyl acetals to provide racemic y9-amino esters in yields up to 99% [104]. 

The carbonyl intermediate then reacts readily with a primary amine to afford an imine and water. A subsequent addition of the iridium hydride to the C=N double bond of the imine, followed by amide-alkoxide exchange, would then occur to release the product. 

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