Evidence for cyclodextrin dioxiranes. Part 2. Catalytic and enantioselective properties of cyclodextrin dioxiranes formed from keto-derivatised hydroxypropyl-cyclodextrins

Following our recent study of the bromine oxidation, at neutral pH, of alph a-cyclodextrin, beta-cyclodextrin, O-methylated beta-cyclodextrins and sucr ose, which yield ketone and carboxylic acid-containing materials in the oxi dation products (M.E. Deary, D.M. Davies, Carbohydr. Res., 309 (1998) 17), we have extended the work to hydroxypropyl-alpha-cyclodextrin and hydroxypr opyl-beta-cyclodextrin. C-13 NMR analysis confirms the presence of ketone g roups (delta 207) in the oxidation products of both of these compounds. The continued ability of the products of these oxidations to complex p-nitroph enol demonstrates that ring integrity is maintained. The ketone-containing products are capable of catalysing the peroxomonosulfate (PMS) oxidation of a range of substrates including aryl alkyl sulfoxides, pyridine, 4-bromopy ridine, aniline, 4-aminobenzoate, 4-bromoaniline and several amino acids, m ost probably by the formation of a more reactive cyclodextrin-dioxirane int ermediate. A small degree of enantioselectivity is observed in the oxidatio n of (R)-(+)- and (S)-(-)-methyl p-tolyl sulfoxide by PMS in the presence o f the keto derivative of hydroxypropyl-alpha-cyclodextrin, though not for t he beta analogue. (C) 1999 Elsevier Science Ltd. All rights reserved.