Hydrolysis iminium cation

Although the [3,3] sigmatropic rearrangement was occurring inside 1, the question of the nature of the hydrolysis remained - does water enter the host cavity and hydrolyze the iminium inside of the assembly or is the iminium cation ejected and hydrolyzed in solution To further understand the hydrolysis mechanism, the... 

From a series of experiments in solutions of pD varying from 6.5 to 12.8 and six equivalents of XMe.b, the buildup and hydrolysis of the iminium cationic intermediate was studied in the rearrangement and hydrolysis of [33 C 1] . In neutral pD (pD 6.5-8), the rates of iminium hydrolysis are essentially constant, with water acting as the nucleophile. However, in more basic solution, a dependence on [OD ] is observed until approximately pD 11, at which point saturation is observed. The observed linear first-order dependence on hydroxide concentration from the pD rage of 9-10.5 supports the mechanistic model where the iminium cation is ejected from the assembly and then hydrolyzed in solution. The presence of saturation implies that, after pD 11, the rate of iminium dissociation from 1 becomes rate limiting because hydrolysis becomes faster than the re-encapsulation process. 

To further probe this pathway, XBu,/, a cation too large to enter 1, was used to displace the ion associated iminium product. As with NMe4+, increasing the concentration of NBU4+ led to faster rates of hydrolysis with a first order dependence on [NBU4+]. With this information, the mechanistic model was proposed that incorporates an intermediate ion associated iminium cation complex (Scheme 7.4). 

Fig. 19 Allyl enammonium salts are encapsulated within the supramolecular assembly, promoting electrocyclization to the corresponding iminium cation. This cation is subject to hydrolysis in basic solution, yielding the aldehyde products while promoting catalytic turnover... 

Sufficiently stable electrogenerated carbenium ions can be trapped with nucleophiles or nucleophilic solvents. Acetoxylation and methoxylation proceed by electrolysis in either acetic acid or methanol. Acetamidation occurs in wet acetonitrile, in which the nucleophilic attack of the nitrile group on the carbenium ions R tends to give iminium cations subsequent hydrolysis with water in the medium completes the reaction ... 

The dependence of the a-deprotonation site on the kinetic acidity of the planar amine radical cation is best demonstrated by the sensitized ET photoreaction of iV-benzyl tertiary amines and A/-alkyl anilines in the presence of DCN, which leads to the efficient Af-debenzylation [38] and A/-dealkylation [39], respectively. These results are explained by considering the hydrolysis of the respective regioselective iminium cations produced during the reaction. The utility of these studies is demonstrated in the A -debenzylation [38] reaction of benzyl-protected tertiary amines and in the understanding of the mechanism of oxidative A -dealkylation [39] of tertiary amines by cytochrome P-450-depen-dent monooxygenases. 

Rueping and Antonchick [51] have examined the phosphoric acid diester-catalyzed 2-aza-Cope rearrangement [52], a transformation that provides an efficient entry to chiral homoallylic amines. They assumed that a phosphoric acid diester would both promote the in situ formation of an allyl iminium cation from an aldehyde and an achiral homoallylic amine, and the subsequent 2-azonia-Cope rearrangement. In a separate hydrolysis step, the rearranged homoallylic amine would furnish the target chiral amine (Scheme 40.42). 

The electrophile 4 adds to the aromatic ring to give a cationic intermediate 5. Loss of a proton from 5 and concomitant rearomatization completes the substitution step. Subsequent hydrolysis of the iminium species 2 yields the formylated aromatic product 3. Instead of the highly toxic hydrogen cyanide, zinc cyanide can be used. The hydrogen cyanide is then generated in situ upon reaction with the hydrogen chloride. The zinc chloride, which is thereby formed, then acts as Lewis acid catalyst. 

Alternatively, a thermal activation of the starting material I would follow the reverse course of its synthesis to furnish cation XVII, which would then undergo a similar spiro cyclization by way of enamine XVIII. The hydrolysis of the ensuing iminium ion would lead directly to the key intermediate XV. 

In the primary reductive step, oxygen from air or Fe(III) ions function as electron acceptor. The radical cation l+ , generated in the oxidative counterpart, loses a proton, affording the strongly reducing a-amino radical (Figure 10), which injects an electron into the conduction band of CdS. Hydrolysis of the resulting iminium salt leads finally to the secondary amine. Repetition of this multi-step reaction affords the completely demethylated product 2. 

Prior to the discoveries that lithium and other less electropositive metal cations were valuable counterions for enolate alkylations, the Stork enamine reaction was introduced to overcome problems such as loss of regioselectivity and polyalkylation that plagued attempts to alkylate sodium or potassium enolates of ketones or aldehydes.Methods of synthesis of enamines by reactions of ketones and aldehydes with secondary amines have been thoroughly reviewed.Enamine alkylations are usually conducted in methanol, dioxane or acetonitrile. Enamines are ambident nucleophiles and C- and V-alkylations are usually competitive. Subsequent hydrolysis of the C-alkylated product (an iminium salt) yields an... 

Vilsmeier acylation of pyrroles, formylation with dimethylformamide/phosphoryl chloride in particnlar, is a generally applicable process. The actual electrophilic species is an Al,Al-diaIkyl-chloromethyleneiminium cation (the chloride is available commercially as a solid). " Here again, the presence of a large pyrrole-A-substituent perturbs the intrinsic a-selectivity, formylation of A-tritylpyrrole favonring the P-position by 2.8 1 and trifluoroacetylation of this pyrrole giving only the 3-ketone " the nse of bulky iV-silyl substituents allows P-acylation with the possibility of subsequent removal of the N-snbstituent." The final intermediate in a Vilsmeier reaction is an iminium salt requiring hydrolysis to prodnce the isolated product aldehyde. When a secondary lactam is used, hydrolysis does not take place and a cyclic imine is obtained." ... 

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