Synthesis of sterically encumbered porphyrins as catalysts for shape-selective oxidations

A general method is described for the synthesis of sterically encumbered po rphyrins whose shielding superstructure can take on the enzymatic role of s ubstrate discrimination. This method is based on an improved synthesis of p yrroles substituted with a 2,6-dibromophenyl group, followed by a Suzuki cr oss-coupling to replace the Br with aryl groups. Porphyrins assembled from such pyrrole units have a barrel shape with the metal center completely fen ced by four beta-substituted terphenyl shielding wings. The Fe and Mn porph yrins prove to be excellent catalysts for regioselective epoxidation of alk enes.