Ketones cyclodextrin, catalysis

Several cyclodextrin ketones with a ketone attached to the secondary face of the cyclodextrin in the form of a 2,3-0-( 1,3-acetone) group (79), and some selected cyclodextrin ketones having the ketone at the primary face, were investigated for their catalysis of epoxidation of stilbenes and styrene by oxone in 1 1 acetonitrile/H20. It was found that secondary face ketones were better catalysts giving a cat uncat over 10, and more stereoselective giving up to 76% ee in (5)-styrene oxide. ... 

Diels-Alder catalysis. Water can accelerate the Diels-Alder reaction of cyclopentad iene with methyl vinyl ketone or acrylonitrile by a hydrophobic interaction. / -Cyclodextrin can increase this effect, possibly because the components can fit into the hydrophobic cavity.1... 

Cyclodextrins with two imidazole groups on the primary hydroxyl side can enhance the enolate formation [86] of a simple bound ketone by bifunctional acid-base catalysis and accelerating the intramolecular aldol condensation of bound ketoaldehyde and dialdehyde. The aldolase mimics which catalyzed crossed aldol condensations were obtained by the assembly of (i-CD and various amino moieties as Schiff base [87]. 

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. 

The participation of the secondary alcoholic functions to the increase in association constant of the ketone recalls the basic catalysis of various esters in aqueous medium. Indeed, this hydrolysis is clearly assisted by j6-CD and Tee et al. present a mechanism in which an ionized hydroxy group of the cyclodextrin acts as a nucleophile towards the guest ester [56]. In several cases the kinetics studies are consistent with a hydrolysis process in which a complex formed from the ester and two molecules of cyclodextrin is involved [57]. 

Much related work has occxured based on organized catalysis in natural and synthetic macrocycles, polymers, and modified surfaces, which can only be hinted at briefly in such a review. We highlight Lehn s application of crown-ethers (83) and (84) in the catalysis of hydrolysis of chiral dipeptide esters (S R up to 50 1) and hydride transfer to ketones, respectively, Knowles s successful preparation of specifically substituted a-cyclodextrins (85) and their involvement in phosphate ester hydrolysis, and Murakami s syntheses of catalytically active p-cyclophanes. " The long-standing contribution of... 

We examined exchange of deuterium into the methyl group of ketone 12 catalyzed by the three isomers of cyclodextrin bisimidazole and also by p-cyclodextrin monoimidazole (5) in D2O solution with 14% CD3OD, buffered at pH 6.2 with phosphate buffer, at 35 °C [12]. We saw essentially no deuterium incorporation into the methyl group over 10 hours with the buffer alone, or the buffer with added simple cyclodextrin. However, all four of the cyclodextrin derivatives (5,6,7, and 8) catalyzed significant deuterium incorporation into the methyl group over the same period. The AB (6) and AC (7) isomers were only marginally more effective than was the monoimidazole catalyst, but the AD isomer 8 was clearly better. A pH vs rate plot for the reaction catalyzed by the AD isomer showed a bell-shaped curve with a rate maximum near pH 6.2, as expected for bifunctional catalysis, while the reaction catalyzed by cyclodextrin-6-imidazole 5 showed a simple increase to a plateau at pH above 7.5, as expected for monofunctional base catalysis. 

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