Threitol-Strapped Manganese Porphyrins as Enantioselective Epoxidation Catalysts of Unfunctionalized Olefins

Nine members of a family of new chiral porphyrins have been prepared from reactions between ditosylthreitol derivatives and 5,10,15,20-tetrakis(2-hydroxyphenyl)porphyrin. The assignment of the resultant isomers has been made from their ¹H NMR spectra and on the basis of an absolute configuration determination from the crystal structure of 4. The chiral frameworks of these systems are easily varied by condensing different aldehydes and ketones with the 2,3-diol of the threitol unit. The manganese derivatives of six of these systems were studied as asymmetric catalysts in the epoxidation of unfunctionalized olefins. Up to 88% ee is obtained in the epoxidation of 1,2-dihydronaphthalene with one of these derivatives, 9, when a bulky imidazole ligand is used to block the unhindered face of the porphyrin catalyst.