THE EFFECT OF CATALYST LOADING AND DONOR LIGANDS IN THE MN(III) SALENCATALYZED CHIRAL EPOXIDATION OF CHROMENES - SYNTHESIS OF BRL-55834

In the absence of a donor ligand both the reaction rate and product e. e. of the manganese (III) salen catalysed epoxidation of 2,2-dimethyl- 6-pentafluoroethylchromene were dependent on the catalyst loading. Iso quinoline N-oxide was the most effective donor ligand, affording highl y efficient epoxidations with catalyst loadings of 0.1-0.4 mol%. These findings allowed the realisation of a concise, inexpensive synthesis of BRL 55834. Copyright (C) 1996 Elsevier Science Ltd