Evidence for cyclodextrin dioxiranes

Solvent effect on the electronic spectra of azine dyes under alkaline condition

Thiazine dye, methylene blue (MB), oxazine dye, nile blue (NB), and phenazine-based dye, neutral red (NR), bear a similar basic dye skeleton with a distinctively different central heteroatom. All of them are extracted into nonpolar organic solvent from alkaline solution. The role of the heteroatom on the respective dye skeletons and redox potentials of the dyes has been examined to signature the stability of the species in organic solvent and the results have been substantiated through geometry optimization and wave function analysis at the density functional theory level. The effect of solvent polarity on the electronic absorption spectra of the three nonionic benzenoid species has been investigated with an intention to investigate the solvatochromic behavior of these compounds.

A cyclodextrin-modified ketoester for stereoselective epoxidation of alkenes

A beta-cyclodextrin-modified ketoester 2 was prepared by covalent attachment of a reactive ketone moiety to beta-cyclodextrin. Treatment of 2 with Oxone as terminal oxidant would produce CD-substituted dioxirane, which can effect stereoselective alkene epoxidation. The 2-mediated (S)-alpha-terpineol epoxidations proceeded to give terpineol oxides in high yields, and the stereoselectivities (i.e., cis-/trans-epoxide ratio) decreased from 2.5:1 to 1:1.2 with increasing steric bulkiness of the terpenes. This steric-dependent stereoselectivity can be understood based on different binding geometries of the 2/terpene inclusion complexes according to the (1)H NMR titration and 2D ROESY experiments. Enantioselective epoxidation of styrenes has also been achieved with 2 as catalyst (20-50 mol %) in aqueous acetonitrile solution, and up to 40% ee was obtained in 4-chlorostyrene epoxidation at 0 degrees C. Similar enantioselectivities were also obtained for the 2-mediated epoxidation of 1,2-dihydronaphthalene (37% ee), 4-chlorostyrene (36% ee), and trans-stilbene (31% ee).