Kemp’s imide

The inability of control molecule (22) to catalyze the reaction allowed us to exclude the Kemp s imide moiety of (6) as a source of direct chemical catalysis (Table 1, entry 8). 

Heating Kemp s acid with appropriate aromatic diamines yields bis-imides with two convergently oriented carboxylic acid groups on the edges of a hydrophobic pocket. Dozens of interesting molecular complexes have been obtained from such compounds and can be traced in the Journal of the American Chemical Society under the authorship of J. Rebek, Jr., (1985 and later e.g. T. Tjivikua, 1990 B). 

Amino-5 -deoxy-2, 3 -0-isopropylideneadenosine was acylated at N-5 with an activated derivative of the 6-carboxy-2-naphthyl ester of Kemp s acid imide. The resulting molecule possesses self-complementary binding sites, the key feature of replicating molecules that act as templates for their own reproduction. The dimer of this molecule is, however, not very stable K = 630 L mol ). When the two initially mentioned educts are added, a small proportion of the ternary complex is also formed and undergoes a fast, template-catalysed... 

The hydrolysis of p-nitrophenyl acetate and bis(p-nitrophenyl phosphate) are frequently used to probe hydrolytic activity. A problem with some other dinuclear systems is that the Zn units are held together by bridging ligands which can be cleaved on reaction with the substrate.440 This is not the case in a ditopic ligand such as those designed by Lippard and co-workers based on Kemp s triacid imide with a xylyl spacer.441,442 Both zinc dimers and mixed metal dimers were formed and a structure characterized with a bridging phosphodiester (Figure 6). 

Scheme 2.8 Examples of ligands used to model the carboxylate coreofcarboxylate-bridged dinuclearironenzymes (a) R3XDK[for R = CH3 H2XDK = m-xylenediamine bis(Kemp s triacid) imide] [57] (b) differently substituted terphenyl-based ligands (e.g. for R1 = CH3, R2 = H TolArCOOH) [48].

Several dinuclear Mn11 complexes based on the dinucleating L9 ligand [L9 = m-xylenediamine bis(Kemp s triacid imide)] have a (p.-carboxylato)2 core [lOOp] (Figure 18). 

Monotrifluoroacetylated diaminopyrazole was first reacted with the free Kemp s triacid to produce the imide, followed by N-Boc protection and amide-coupling with a m-substituted aniline derivative. Final Boc-deprotection occurred on the chromatography column leading directly to the new receptor modules. The recognition site X was chosen to be ethyl as a neutral reference, acetyl for polar side-chains, nitro for electron-rich aromatic residues and carboxylate for basic amino acids (Figure 2.4.4). 

Double stereodifferentiation was effective in the protonation of the lithium enolate of (—)-menthone using chiral imides derived from Kemp s triacid. This protonating agent gathers both the chelation with the chiral oxazoline and a cumbersome protonating imide site. Moreover, a catalytic version was set up using 0.1 equivalent of the chiral imide in the presence of a non-chiral proton source (Scheme 73)357,358. 

SCHEME 73. Catalytic cycle in the protonation of 2-isopropyl-5-methyl cyclohexanone lithium enolate using Kemp s acid imide derivative as a catalyst357,358... 

Chiral bis(oxazolines) 51 with an oxalylic acid backbone were used for the Ru-catalyzed enantioselective epoxidation of tran5-stilbene yielding franx-l,2-diphenyloxirane in up to 69% ee [24]. The asymmetric addition of diethylzinc to several aldehydes has been examined with ferrocene-based oxazoline ligand 52 [25], resulting in optical yields from 78-93% ec. The imide 53 derived from Kemp s triacid containing a chiral oxazoline moiety was used for the asymmetric protonation of prochiral enolates [26]. Starting from racemic cyclopentanone- and cyclohexanone derivatives, the enantioenriched isomers were obtained in 77-98 % ee. 

The final iron cage discussed is the largest known ferric wheel. The octadecanuclear wheel, [Fe(0H)(XDK)Fe2(0Me)4(02CMe)2]e (70) [XDK = the dianion of m-xylylenediamine bis(Kemp s triacid imide) see Scheme 2] (164), shown in Fig. 29, is made from reaction of the di-nuclear iron complex of XDK with [NEt4](02CMe) in methanol, followed... 

The initial self-replication system investigated involved recognition between adenine and an imide of Kemp s triacid via hydrogen bond formation. The... 

Complexes incorporating a constrained bis-carboxylate ligand, ZrX2(XDK) (X = Bn, NMe2 XDK = m-xylylenediamine bis(Kemp s triacid imide)) and Zr(XDK)2 have been synthesized and characterized structurally. This ligand was derived from Kemp s tri-acid imide derivative of m-xylylenediamine (92) and shown to chelate through the two carboxylic acid fragments.483... 

Our research group independently found a catalytic enantioselective proto-nation of preformed enolate 47 with (S,S)-imide 30 founded on a similar concept (Scheme 5) [51]. The chiral imide 30, which has an asymmetric 2-oxazoline ring and is easily prepared from Kemp s triacid and optically active amino alcohol, is an efficient chiral proton source for asymmetric transformation of simple metal enolates into the corresponding optically active ketones [50]. When the lithium enolate 47 was treated with a stoichiometric amount of the imide 30, (K)-en-riched ketone 48 was produced with 87% ee. By a H-NMR experiment of a mixture of (S,S)-imide 30 and lithium bromide, the chiral imide 30 was found to form a complex rapidly with the lithium salt. We envisaged that a catalytic asym-... 

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