One‐Pot Multimolecular Macrocyclization for the Expedient Synthesis of Macrocyclic Aromatic Pentamers by a Chain Growth Mechanism

POCl(3)-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.