An efficient synthesis of highly functionalized asymmetric porphyrins with organolithium reagents

Abstract

Functionalized tri- (A₂B-type) and tetra- (A₂BC-type) meso-substituted asymmetric porphyrins bearing highly reactive centers like -NH₂, -OH, -CCH, -CHO in substituents at the meso positions were synthesized in good yields via the reaction of 5,15-diphenylporphyrin with corresponding functionalized organolithium reagents. Through further transformation other functional groups like carboxylate, iodophenyl, thiocarboxylate, tertiary amines and quaternary ammonium salts are easily available. Such porphyrins serve as precursors for highly complex tetrapyrrolic systems. As examples, several novel porphyrins with potentially useful chemical and physical properties such as amphiphilicity, water solubility, and electrochemical redox activity were synthesized. In contrast to existing methods such compounds are now accessible regioselectively via one-step or two-step reactions in high yields. In addition, protocols were developed to prepare porphyrins with meso-aryl substituents bearing functional groups at the para, meta, or ortho position. Thus, starting materials for various specifically superstructured tetrapyrroles are available via rational syntheses.