Enantioselective epoxidation of non-functionalised alkenes using a urea–hydrogen peroxide oxidant and a dimeric homochiral Mn(III)-Schiff base complex catalyst

Abstract

The catalytic enantioselective epoxidation of chromenes, indene and styrene using a urea–hydrogen peroxide adduct as an oxidising agent and the novel dimeric homochiral Mn(III)-Schiff base catalyst 1 has been investigated in the presence of carboxylate salts and nitrogen and oxygen coordinating co-catalysts. Conversions of more than 99% were obtained with all alkenes except styrene. Absolute chiral induction, as determined by 1H NMR using the chiral shift reagent (+)-Eu(hfc)3, was obtained in the case of nitro- and cyanochromene. The catalyst could be re-used for up to five cycles with some loss of activity due to degradation of the catalyst under epoxidation condition with retention of e.e.'s.