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

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-c atalysts. Conversions of more than 99% were obtained with all alkenes excep t styrene. Absolute chiral induction, as determined by H-1 NMR using the ch iral shift reagent (+)-Eu(hfc)(3), was obtained in the case of nitro- and c yanochromene. The catalyst could be re-used for up to five cycles with some loss of activity due to degradation of the catalyst under epoxidation cond ition with retention of e.e.'s. (C) 2001 Elsevier Science Ltd. All rights r eserved.