Hexaalkyl Terpyrrole: A New Building Block for the Preparation of Expanded Porphyrins

Abstract

A new, general synthesis of the first β‐substituted tetra‐ and hexaalkyl terpyrroles is described. Also described are two new classes of expanded porphyrins derived from the hexaalkyl terpyrrole. The key step in the terpyrrole formation is the copper(II)‐mediated oxidative coupling of the LDA‐derived enolates of α‐keto pyrroles. The first new expanded porphyrin reported here, the so‐called “orangarin”, contains five pyrrolic subunits and two bridging carbon atoms, and is formally a 20π‐electron nonaromatic macrocycle. The second new class of expanded porphyrins, the “amethyrins”, are 24π‐electron nonaromatic macrocycles containing six pyrrole units. Both of these new macrocycles, as well as one of the new terpyrrolic precursors have been structurally characterized by single crystal X‐ray diffraction analysis.