Synthesis and activity of macrocyclized chiral Mn(III)–Schiff-base epoxidation catalysts

A series of chiral macrocyclic Mn(III)Salen complexes has been prepared with two salicylidene moieties linked in their 3 and 3′ positions by aliphatic polyether bridges of variable lengths or by a more rigid aromatic junction arm. X-ray structures of ligand precursors and of complex 8 have been performed. All complexes have been used in the asymmetric epoxidation of 1,2-dihydronaphthalene with NaOCl as oxygen atom donor and exhibited modest enantiomeric excesses. Complex 10 was selected to be tested with two cis-disubstituted olefins and several oxidants, namely NaOCl, PhIO and n-Bu4NHSO5. 2,2′-Dimethylchromene oxide was obtained from 2,2′-dimethylchromene with ee values of 56% and 74% when using 10 and NaOCl and PhIO, respectively.

Graphical abstractA series of chiral macrocyclic Mn(III)Salen complexes has been prepared with two salicylidene moieties linked in their 3 and 3′ positions by aliphatic polyethers bridges of variable lengths or by a more rigid aromatic junction arm, in order to study the flexibility of the linkers in asymmetric catalysis. These complexes have been tested in the asymmetric epoxidation of cis-disubstituted olefins with several oxygen atom donors.Figure optionsDownload full-size imageDownload as PowerPoint slide