Combining the Diaza‐Diels–Alder Reaction and Palladium‐Catalyzed Aminations to Prepare Amino‐Substituted Porphyrins

Abstract

AbstractA strategy to tackle the synthesis of azoporphyrins with unsubstituted terminal meso positions was investigated. It comprised the combination of diaza‐Diels–Alder (DADA) reaction of 1,3‐dienes with dialkyl azodicarboxylates, decarboxylative hydrolysis of the bis(carbamates), palladium‐catalyzed amination of bromoporphyrin precursors, and retro‐DADA reactions to release the ultimate targets. The somewhat confused historical results on the DADA reactions of 1,3‐cyclohexadiene were clarified, but the hydrolyses yielded extremely air‐sensitive amines which decomposed completely in minutes via autooxidation and retro‐DADA reaction. With anthracene or 2,3‐dimethyl‐1,3‐butadiene as the diene, the synthesis of azoporphyrin was not achieved but three amino‐substituted porphyrins were obtained in moderate yields under mild conditions. The X‐ray crystal structures of several of the intermediates and the final aminoanthracene‐porphyrin nickel(II) complex were determined.