Exchange reactions, imine

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... 

Imine metathesis has continued to be a popular exchange reaction for DCLs. Various groups have found novel systems in which the reaction can be applied, as well as interesting ways to halt the equilibration. For example, Wessjohann and coworkers have demonstrated that Ugi reactions can efficiently halt equilibration of an imine DCL, combining an irreversible diversification process with areversible library selection [24]. Xu and Giusep-pone have integrated reversible imine formation with a self-duplication process [25], and Ziach and Jurczak have examined the ability of ions to template the synthesis of complex azamacrocycles [26]. The mechanistically related reactions of hydrazone [27] and oxime [28] exchange have also been explored as suitable foundations for DCL experiments. 

One can in principle combine different exchange reactions in the same system in order to further increase the structural diversity accessed by the library. However, as this compounds the problem of selectivity (i.e., one now has two or more reactions that must exclusively involve one pair of functional groups), there are very few examples thus far of the practical implementation of this concept. An early, highly intriguing example was described by Lehn and coworkers in 2001 [68]. In this system, imine exchange (acyl hydrazone formation) and reversible metal coordination were employed in library generation. 

TSlot recombined through the imine exchange reaction hut just blended. Source Reference 25. 

Reductive -elimination of A3-iodanes on carbon atoms (M = C) produces C-C double bonds, while that on oxygen and nitrogen atoms (M = O and N), combined with the initial ligand exchange reaction, provides a method for oxidation of alcohols and amines to the corresponding carbonyl compounds and imines, respectively [Eq. (26)]. 

The regioselectivity of the double nucleophilic addition of ketene silyl acetals to a,/3-unsaturated imines has been found to be highly dependent on the subtle difference in the reactivities of the ketene silyl acetals the factors are mainly derived from the ability of the ketene silyl acetals to undergo the silicon-aluminium exchange reaction, where the aluminium enolate preferentially undergoes 1,4-addition.209... 

In contrast with 17, complex 21 (Scheme 1.18) did not undergo ligand substitution with the copper(I) bis(biquinoline) complex, possibly as a result of the different steric properties of the two complexes. The imine exchange reaction with phenylenediammonium worked well, creating the possibility of a new kind of domino or cascade reaction (Scheme 1.18). The intermediate product 18 (from... 

The proposed mechanism for this catalytic asymmetric hydrophosphonylation is shown in Figure 35. The first step of this reaction is the deprotonation of dimethyl phosphite by LPB to generate potassium dimethyl phosphite. This potassium phosphite immediately coordinates to a lanthanoid to give I due to the strong oxophilicity of lanthanoid metals. The complex I then reacts (in the stereochemistry-determining step) with an imine to give the potassium salt of the a-aminophosphonate. A proton-exchange reaction affords the product... 

The imines (CFa)2C=NH and (CFa)2S=NH are convincing examples for this carbon-sulfur exchangeability. Reactions of the two imines with RLi, RC1, C1F, as well as photolysis, hydrolysis, and their preparation are similar and take place according to Table I. 

Fig. 27 Examples of thermodynamically controlled reactions employed in the near-quantitative synthesis of MIMs. (a) Disulfide-exchange reaction permits equilibration between a bis(ammo-nium) disulfide dumbbell and a crown ether macrocycle to yield a mixture of [2]- and [3]rotaxanes quantitatively [194], (b) Olefin metathesis at high concentration on a benzylic amide macrocycle greatly favors the catenated species [196]. (c) Self-correcting imine bonds allow for nearly quantitative selection of a [2]rotaxane from an appropriate dynamic combinatorial library [76], (d) A weak nucleophile (E) equilibrates the components of a donor-acceptor [2]catenane in a dynamic Sn2 reaction [205]...

Scheme 11 Model reversible aminonitrile reactions exchange reactions with (a) imine and (b) amine...

In 1992, Goodwin and Lynn reported the first example of template-directed synthesis of DNA analogs via formation of a reversible imino linkage [21]. Five years later, Hue and Lehn described the first use of the reaction of imine condensation for the selection, by DCC, of carbonic anhydrase inhibitors from a library of amines and aldehydes [8], Upon addition of the enzyme, the formation of one library component was strongly amplified when compared to a similar reaction carried out in the absence of template. Since then, imine exchange reaction has been applied... 

Amine Exchange Reaction of a g-Keto Imine with an Amine in the Presence of a Metal Ion... 

Chelate Exchange. Metal derivatives of j3-keto imines can be prepared by a chelate-exchange reaction (synthesis 1). 

This reaction is analogous to the preparation of bis(4-imino-2-pentanonato)copper(II) [bis(4-amino-3-penten-2-onato)copper(II)] described by Holtzclaw, Collman, and Alire, and it consists in mixing an ethanolic solution of the -keto imine ( -imino ketone) with an ammoniacal metal salt solution. Advantages of this technique are the simplicity of preparation and the fact that acetylacetone imide (4-imino-2-pentanone) can be purchased. The product is useful as a starting material in ligand-exchange reactions. 

Heterobimetallic catalysis mediated by LnMB complexes (Structures 2 and 22) represents the first highly efficient asymmetric catalytic approach to both a-hydro and c-amino phosphonates [112], The highly enantioselective hydrophosphonylation of aldehydes [170] and acyclic and cyclic imines [171] has been achieved. The proposed catalytic cycle for the hydrophosphonylation of acyclic imines is shown representatively in Scheme 10. Potassium dimethyl phosphite is initially generated by the deprotonation of dimethyl phosphite with LnPB and immediately coordinates to the rare earth metal center via the oxygen. This adduct then produces with the incoming imine an optically active potassium salt of the a-amino phosphonate, which leads via proton-exchange reaction to an a-amino phosphonate and LnPB. 

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