Durene-capped porphyrins: synthesis and characterization

The synthesis of porphyrins having a fully hydrophobic cavity capped by a durene moiety is described. The size of the cavity is adjusted by varying the number of methylene -(CH 2 ) n - groups linking the tetramethylphenylene cap with the diametrically opposite β-positions of the porphyrin. Bis(chloromethyl)durene ( 1 ) was first converted to durene-bisalkanoic acids 11 (n = 4), 13 (n = 5), and 18 (n = 7) using standard chain extension methods. The diacid chlorides were then used to acylate two equivalents of a β-unsubstituted pyrrole to give a chain-linked bispyrrole. Each pyrrole, following appropriate manipulation of the α substituents, was condensed with an α-unsubstituted pyrrole and the resulting chain-linked dipyrromethane dimer was cyclized intramolecularly under high dilution to give the capped porphyrin 34 (n = 4, 5, or 7).