Cyclodextrin, supramolecular catalysis

Aldehydes have been allylated with allyltributyltin, using supramolecular catalysis in acidic water at 60°C.196 Using j3-cyclodextrin as catalyst with all species at a 1 mmol level, high yields were obtained in a few hours. The catalyst, which can be recycled effectively, hydrogen bonds the aldehyde oxygen within the cavity. 

The use of cyclodextrins14 has provided the ability to conduct the Strecker reaction with TMSCN in water via supramolecular catalysis involving reversible guest-host interactions. Activation of imine 16 by complexation with the hydroxyl groups present in cyclodextrins was found to work best with p-cyclodextrin. This chemically green reaction could be applied to ketones as well as aldehydes. 

R. Sridhar, B. Srinivas, K. Surendra, N. S. Krishnaveni, K. R. Rao, Synthesis of j8-hydroxy selenides using benzeneselenol and oxiranes under supramolecular catalysis in the presence of /3-cyclodextrin in water, Tetrahedron Lett, 2005, 46, 8837-8839. 

M. S. Raddey, B. Srinivas, R. Sridhar, M. Narender, K. R. Rao, Highly regioselective thiolysis of oxiranes under supramolecular catalysis involving j8-cyclodextrin in water, J. Mol. Catal. A. Chem., 2006, 255, 180-183. 

Supramolecular chemistry has been a very popular research topic for three decades now. Most applications are foreseen in sensors and opto-electronical devices. Supramolecular catalysis often refers to the combination of a catalyst with a synthetic receptor molecule that preorganizes the substrate-catalyst complex and has also been proposed as an important possible application. The concept, which has proven to be powerful in enzymes, has mainly been demonstrated by chemists that investigated hydrolysis reactions. Zinc and copper in combination with cyclodextrins as the receptor dramatically enhance the rate ofhydrolysis. So far, the ample research devoted to transition metal catalysis has not been extended to supramolecular transition metal catalysis. A rare example of such a supramolecular transition metal catalyst was the results of the joined efforts of the groups of Nolte and Van Leeuwen [SO], They reported a basket-shaped molecule functionalized with a catalytically active rhodium complex that catalyzed hydrogenation reactions according to the principles of enzymes. The system showed substrate selectivity, Michaelis Menten kinetics and rate enhancement by cooperative binding of substrate molecules. The hydroformylation of allyl catachol substrates resulted in a complex mixture of products. 

Khalili B, Jajarmi P, Efiekhari-Sis B, Hashemi MH (2008) Novel one-pot, three-component synthesis of new 2-alkyl-5-aryl-(fH)-pyrrole-4-ol in water. J Org Chem 73 2090-2095 Murthy SN, Madhav B, Kumar AV, Rao KR, Nageswar YVD (2009) Multicomponent approach towards the synthesis of substituted pyrroles under supramolecular catalysis using P-cyclodextrin as a catalyst in water under neutral conditions. Helv Chim Acta 92 2118-2124 Pan L, Bi X, Liu Q (2013) Recent developments of ketene dithioacetal chemistry. Chem Soc Rev 42 1251-1286... 

Supramolecular catalysts using synthetic host molecules have been well researched. Early studies realized a hydrolysis reaction for ester derivatives using modified cyclodextrins (CDs). CDs are suitable for the study of two-substrate supramolecular catalysis and for the synthesis of artificial enzymes. 2-Benzyimidazoleacetic acid-modified a-cyclodextrin hydrolyzes m-tert-butylphenyl acetate at an accelerated rate. The imidazole has a benzoate group in a position that imitates the function of the aspartate ion with the catalytic triad characteristics of serine proteases such as chymotrypsin (Figure 12.1). ... 

In recent years, supramolecular chemistry has produced a number of systems which have been shown to be able to effectively catalyze a Diels-Alder reaction. Most systems selectively afforded only one diastereomer because of a pre-organized orientation of the reactants. These systems include cyclodextrines, of which applications in Diels-Alder chemistry have recently been reviewed89. Some other kinds of non-Lewis acid catalyzed Diels-Alder reactions, including catalysis by proteins and ultrasound, have been discussed by Pindur and colleagues90. 

This short compilation of the recent literature results convincingly demonstrates the usefulness of water-soluble supramolecular complexing agents in biphasic aqueous organometalHc catalysis. Due to their availability, cyclodextrins play a major role in this field. Thinking of the relatively low price of these chemicals (a few per kg in 1998 [2]) their use on a larger scale can also be envisaged in fine chemicals production. 

Lacroix. T. Bricout. H. Tilloy. S. Monflier. E. Chemically modified P-cyclodextrins as supramolecular carriers in the biphasie palladium-catalyzed cleavage of allylic substrates Activity enhancement and substrate-selective catalysis. Eur. J. Org. Chem. 1999. 3127—3129. 

Reetz, M.T. Waldvogel. S.R. P-Cyclodextrin-modified dipliosphane as ligands for supramolecular rhodium catalysis. Angew. Chem., Int. Ed. 1997. 36. 865-867. 

The catalytic properties of the sulfonated diphosphine-stabilized RuNPs and sulfonated diphosphine/cyclodextrin-stabilized RuNPs were compared in the hydrogenation of unsaturated model substrates (styrene, acetophenone, and w-methylanisole) in biphasic liquid-hquid conditions (i.e., ruthenium aqueous colloidal solution and organic substrate no added solvent). Whilst all of these RuNPs displayed suitable performances in catalysis, different activities and selec-tivities were observed. This highhghted that supramolecular interactions on the metallic surface in the presence of a cyclodextrin control the catalytic reactivity of the nanocatalysts. Interestingly the CD acts as a phase-transfer promotor, which... 

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