One-pot multimolecular macrocyclization for the expedient synthesis of macrocyclic aromatic pentamers by a chain growth mechanism

Abstract

POCl3-mediated one-pot macrocyclization allows the highly selective formation of five-residue macrocycles that are rigidified by internally placed intramolecular hydrogen bonds. Mechanistic investigation by using tailored competition experiments and kinetic simulation provides a comprehensive model, supporting a chain-growth mechanism underlying the one-pot formation of aromatic pentamers, whereby the successive addition of a bifunctional monomer unit onto either another monomer or the growing oligomeric backbone is faster than other types of bimolecular condensations involving oligomers longer than monomers. DFT calculations at the B3LYP/6-31G* level reveal the five-residue pentamer to be the most stable with respect to alternative four-, six-, and seven-residue macrocycles. These novel mechanistic insights may become useful in analyzing other macrocyclization, oligomerization, and ploymerization reactions. Adding one by one: POCl3-mediated one-pot macrocyclization allows the highly selective formation of five-residue macrocycles that proceeds by a chain-growth mechanism in which the successive addition of a bifunctional monomer unit onto either another monomer or the growing oligomeric backbone is faster than other types of bimolecular condensations involving oligomers longer than monomers (see scheme). © 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim.