Kinetic imine

The hydrolysis of simple imines occurs readily in aqueous acid and has been studied in great detail by kinetic methods. The precise mechanism is a fimction of the reactant structure and the pH of the solution. The overall mechanism consists of an addition of water to the C=N bond, followed by expulsion of the amine from a tetrahedral intermediate. ... 

Analysis of the kinetics of this catalysis points to the protonated imine as the key intermediate. 

The kinetics of the hydrolysis of some imines derived from benzophenone anc primary amines revealed the normal dependence of mechanism on pH with ratedetermining nucleophilic attack at high pH and rate-determining decomposition of the tetrahedral intermediate at low pH. The simple primary amines show a linear correlation between the rate of nucleophilic addition and the basicity of the amine Several diamines which were included in the study, in particular A, B, and C, al showed a positive (more reactive) deviation from the correlation line for the simple amines. Why might these amines be more reactive than predicted on the basis of thei ... 

Assume that the steady-state approximation can be applied to the intermediate TI. Derive the kinetic expression for hydrolysis of the imine. How many variables must be determined to construct the pH-rate profile What simplifying assumptions are justified at very high and very low pH values What are the kinetic expressions that result from these assumptions ... 

Reaction of 2-(A -alkyl-A -benzylamino)- and 2-[A -(rraM-crotyl)-A -ben-zylamino]-3-formyl-4/7-pyrido[l,2-n]pyrimidin-4-ones (260, R = H, Me) with tosylamine gave compounds 268 via compounds 266 and 267 (96T13097). The results of kinetic studies and MP3 calculations on the 3-formyl derivatives 252, 260 and the imines 262, 263 suggested a concerted nature for azepine-ring formation. 

Both primary and secondary amines add to a /S-unsaturated aldehydes and ketones to yield /3-amino aldehydes and ketones rather than the alternative imines. Under typical reaction conditions, both modes of addition occur rapidly. But because the reactions are reversible, they generally proceed with thermodynamic control rather than kinetic control (Section 14.3), so the more stable conjugate addition product is often obtained to the complete exclusion of the less stable direct addition product. 

This contrary stereochemistry in the Bucherer - Bergs reaction of camphor has been attributed to steric hindrance of e.w-attack of the cyanide ion on the intermediate imine. Normally, equatorial approach of the cyanide ion is preferred, giving the axial (t>Mr/o)-amino nitrile by kinetic control. This isomer is trapped under Bucherer-Bergs conditions via urea and hydan-toin formation. In the Strecker reaction, thermodynamic control of the amino nitrile formation leads to an excess of the more stable compound with an equatorial (e.w)-amino and an axial (endo)-cyano (or carboxylic) function13-17. 

The reaction parameters of the alcoholysis of A A -bis(diphenylphos-phino)-5 5-dimethylsulphocii-imine (93), to give 5 5-dimethylsulphodi-imine (94), have been determined by a kinetic study using n.m.r. ... 

Coles, B., Wilson, I. and Wardman, P. (1988). The spontaneous and enzymatic reaction of N-acetyl-/>-benzoquinone imine with glutathione, a stopped flow kinetic study. Arch. Biochem. Biophys. 264, 253-260. 

Ketone imine anions can also be alkylated. The prediction of the regioselectivity of lithioenamine formation is somewhat more complex than for the case of kinetic ketone enolate formation. One of the complicating factors is that there are two imine stereoisomers, each of which can give rise to two regioisomeric imine anions. The isomers in which the nitrogen substituent R is syn to the double bond are the more stable.114... 

Y(03SCF3)3 to afford a monoaminoalkylation product in good yield in aqueous media.40 Zinc tetrafluoroborate is also highly effective for such couplings in aqueous THF.41 Kobayashi also reported a Mannich-type reaction of imines with silyl enolates catalyzed by neutral salts such as sodium triflate in water as a suspension medium. Unusual kinetic behavior indicates that the presence of the Mannich adduct facilitates the rate of its formation.42... 

Whether the [2+2] or [2+4] cycloaddition product is formed in the first reaction depends on the reaction conditions however, one product is convertible to the other via the silene intermediate. In the other reactions shown, the identity of the product formed, [2+2] or [2+4], seemed to be a function of the structures of both the silene and imine. In the last case, the [2+4] product appeared to be the kinetic isomer since conversion to the [2+2] isomer slowly occurred on standing in the dark, or faster if photolyzed, even at room temperature. 

Wiberg has studied the kinetics of several systems involving the silene Me2Si=C(SiMe3)2. The kinetics for the complex system of the silene with jV-trimethylsilylbenzophenonimine, namely [2+4] adduct <=> silene + imine <=> [2+2] adduct as shown in Eq. (62), were measured174,198 as were the data for the corresponding system with benzophenone, viz. [2+4] adduct <=> silene + benzophenone <=> [2+2] adduct.220... 

Compounds of types i, 2, and 3 were deduced to have planar, trigonal configurations from kinetic and stereochemical observations71 however, confirmation of this postulate was provided only a few years ago by the X-ray structure analysis of (bistrimethylsilyl)aminobis(trimethylsilylimino)phosphorane8). The P/N(imine) bonds were found to be relatively short, which was attributed to a high rc-bonding component in the planar system of coordinatively unsaturated phosphorus. 

Pr(H2)CPPh3)2(solv)2]+ catalysts for imine hydrogenation have been kinetically explored. This area is notably less developed than the reduction of C=0 bonds.88,110... 

In a study by Leitner of the iridium-catalyzed hydrogenation of imines, a nearly 20-fold increase in catalytic efficiency was observed due to a different kinetic profile in scC02 as compared to methylene chloride.358 The change in rate and selectivity found in scC02 with respect to the other solvents can be related to the following major points ... 

Some theoretical aspects of thiophene reactivity and structure have also been discussed, for example the kinetics of proton transfer from 2,3-dihydrobenzo[6]thiophenc-2-onc <06JOC8203>, the configuration of imines derived from thiophenecarbaldehydes <06JOC7165>, and the relative stability of benzo[c]thiophene <06T12204>. The kinetics of nucleophilic aromatic substitution of some 2-substituted-5-nitrothiophenes in room temperature ionic liquids have also been investigated <06JOC5144>. 

An unusual temperature dependence on the regioselective behavior of an allylbarium species has been demonstrated in asymmetric allylation with the optically active imine SAMP-hydrazone [SAMP = (A)-(—)-l-amino-2-meth-oxymethylpyrrolidine] (Scheme 10).322 Its reaction with prenylbarium chloride at 0°C produced an a-allylated hydrazine in 60% diastereotopic excess, but at — 78 °C, the y-adduct was generated with 98% diastereotopic excess. The temperature dependence of the ct/y ratio may reflect competition between a kinetically favored y-adduct at low temperature and a thermodynamically preferred ct-form at higher temperatures. 

This catalytic system can be used for the kinetic resolution of di-substituted 1-pyrrolines, for which high ee-values are achieved for both the amine and the recovered materials, especially when they are substituted in positions 2 and 5 (Table 6.6) [111]. Moreover, it should be noted that acyclic enamines are converted with high ee-values into their corresponding amines (89-98% ee Table 6.7), which is in sharp contrast to what is obtained for acyclic imines (vide supra) [112]. 

Kinetic resolution results of ketone and imine derivatives are indicated in Table 21.19. In the kinetic resolution of cyclic ketones or keto esters, ruthenium atrop-isomeric diphosphine catalysts 25 induced high enantiomer-discriminating ability, and high enantiopurity is realized at near 50% conversion [116, 117]. In the case of a bicyclic keto ester, the presence of hydrogen chloride in methanol served to raise the enantiomer-discriminating ability of the Ru-binap catalyst (entry 1) [116]. 

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