Research On Phase Transfer Catalytic Epoxidation Of Enone

Trichloroisocyanuric acid has been recognized as a mild and efficient oxidant for both liquid-liquid and solid-liquid biphasic phase transfer catalytic epoxidation of enone, and selective oxidation of alcohols to aldehydes and ketones without any catalyst under non-aqueous condition.Initial experiment showed clearly that trichloroisocyanuric acid is a good oxidant for liquid-liquid biphasic phase transfer catalytic epoxidation of enone in the presence of inorganic base and phase transfer catalyst. The condition optimization of enantioselective epoxidation has been carried out using chiral quaternary ammonium salt derived from cinchona alkoids as a phase transfer catalyst. Treatment chalcone derivatives with TCCA under mild conditions afforded the corresponding epoxides in good yields with moderate to excellent enantioselectivities. Up to 96% ee was achieved with 4-nitro-chalcone as enone substrate. In a number of cases the crude reaction products were most conveniently purified by recrystallisation, giving the epoxides up to 99% ee.A non-aqueous procedure of phase transfer catalytic epoxidation of enone has been developed with trichloroisocyanuric acid as a readily available alternative to the commonly used hydrogen peroxide and hypochlorite. The new procedure is much convenient for products separation excluding the wet viscid isocyanuric acid. A variety of chalcone derivatives give the corresponding epoxides with quantitative conversion and satisfactory yields in just a few hours under very mild conditions. Asymmetric variant of the epoxidation can be carried out in the presence of chiral N-anthracenylmethyl chinconidine bromide catalyst in 83-93% ees and 76-94%yields.A non-aqueous selective oxidation of active alcohols to aldehydes and ketones has been developed with trichloroisocyanuric acid as a highly efficient oxidant without any catalyst in the presence of inorganic base. The electron-withdrawing functional groups in the benzyl alcohols favor the oxidation, and the substrate with pyridine can also proceed to oxidize smoothly. This provides a convenient method for the selective oxidation of alcohols to aldehydes and ketones.