Imine metathesis

Table 2 Equilibrium constants for various imine metathesis reactions ...

As we have already mentioned, the ability of imine formation to serve as a useful reaction in templated systems was observed by Lynn et al. in the early 1990s. Use of imine metathesis in DCC was first described by Hue and Lehn in 1997 in a library targeting the production of carbonic... 

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. 

Scheme 8.1 Imine metathesis polymerizations of 1 and 2 in CH CN and CHCl and their reversible featnre [17,18],...

Figure 8.2 Schematic representation of the imine metathesis polymerization of 1 and 2 driven by folding of resnlting polymer 3 [17,18].

D. Zhao, J. S. Moore, J. Org. Chem. 2002, 67, 3548-3554. Imine metathesis reactions in different solvents suggest that the formation of assemblies of stacked rings is the thermodynamic driving force for the exclusive cyclodimer formation D. Zhao, J. S. Moore, Macromolecules 2003, 36, 2712-20. 

In the early 1960s, seminal work by Jencks and coworkers demonstrated that formation and hydrolysis of C=N bonds were proceeding via a carbinolamine intermediate, thus leading to a more general mechanism of addition reactions on carbonyl groups [17-19]. The dynamic nature of the reaction of imine formation can be exploited to drive the equilibrium either forward or backwards. Since the reaction involves the loss of a molecule of water, adding or removing water from the reaction mixture proved an efficient way to shift the equilibrium in either direction. The responsive behavior of imines to external stimuli makes the reversible reaction of imine formation perfectly suited for DCC experiments [20], Thermodynamically controlled reactions based on imine chemistry include (1) imine condensation/hydrolysis, (2) transiminations, and (3) imine-metathesis reactions... 

Fig. 1 Three examples of reversible reactions involving imines (i) inline condensation/hydrolysis (ii) transimination, and (iii) imine metathesis reaction...

The complex ReMe(NAd)s exchanges NAd for O with aldehydes, not ketones, to form ReMe03 and RCH=NAd. It also exchanges NAd for NR with imines RCH=N (imine metathesis). ... 

Imine metathesis. Two imines containing different groups give equimolar mixtures of four possible imines. 

Scheme 207). Diazametallacycles such as 831 are key intermediates involved in imine metathesis catalyzed by zirconocene imido complexes,628 the authentic samples of which were synthesized independently by the reaction of 825 with 2 equiv. of the corresponding imine.629 The zirconocene imido complex 825 also ring-opens epoxides such as styrene oxide regioselectively to give metallacycle 832 (Scheme 207).630... 

The metallocene complex 27 containing a M=X double bond undergoes overall [2 + 2] cycloaddition with an internal alkynes to give heterometallacyclobutenes (28) [77], A formal [2 + 2] cycloaddition of CpjZr (=N Bu)(thf) with imine affords a 2,4-diazametallacyclobutane, whose further reaction with imines results in an imine metathesis reaction [78] azametallacyclobutene is an intermediate in the Cp2Zr(NHR)2-assisted hydroamination of alkynes and allene [79],... 

Benzylideneanilines have been added across 2,3-dihydrofurans to produce bicyclic azetidines regio- and stereoselectively a zwitterionic mechanism is proposed. An extensive range of reaction parameters have been calculated for the Mannich reaction of benzoxazole with formaldehyde/dimethylamine. A molybdenum bis(imide) has been used to catalyse C=N bond formation in imine-imine metathesis reactions of synthetic interest the approach has been extended to alkylidene-imine, imide-imine, and imide-imide metatheses. 1-Substituted 1-phenyl-... 

Scheme 17 Effect of the addition of hexylamine to the DLs previously generated by imine metathesis of compounds 9 at low concentrations.

CiacciaM, Cacciapaglia R, MencareUi P, Mandolini L, Di Stefano S. Fast transimination in organic solvents in the absence of proton and metal catalysts. A key to imine metathesis catalyzed by primary amines under rmld conditions. Chem Sci. 2013 4 2253-2261. 

Ciaccia M, Pdati S, Cacciapagha R, Mandolini L, Di Stefano S. Effective catalysis of imine metathesis by means of fast transiminations between aromatic-aromatic or aro-matic-abphatic amines. Org Biomol Chem. 2014 12 3282-3287. 

Folding-driven synthesis of oligomers and polymers of m-phenyleneethynylene has been reported in the reversible imine metathesis reaction of an N-terminal imine dimer and hexamer with a C-terminal imine hexamer, formation of the longer 12-mer was favored over other species in acetonitrile while lower oligomers were largely formed in chloroform. ... 

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