New strategies for the synthesis of substituted magnesium porphyrins

Porphyrins are valuable compounds for studies in biomimetic and materials chemistry. Efficient routes for the synthesis of porphyrins bearing distinct types and patterns of substituents are essential for such studies and for diverse applications.;A new set of conditions has been developed for the synthesis of a broad class of porphyrins. The conditions entail a metal salt MgBr2, and a non-coordinating base DBU in a non-coordinating solvent (toluene) with heating (conventional or microwave irradiation) in the presence of air.;The reaction of 1-formyldipyrromethane under such basic, Mg-mediated conditions afforded Mg(II)porphine in 30--40% yield. The advantages of the new method include simplicity, high concentration, chromatography-free purification, gram-scale synthesis, and avoidance of the poorly soluble free base porphine (Chapter 1).;New methodology is described for the synthesis of porphyrins bearing four (A4, cis-A2B2, cis-ABC2, trans-A2B2 ) or fewer (A, cis-AB, cis-A 2, trans-A2) meso-substituents. The rational synthesis of trans-A2B2- or trans-A2-porphyrins was achieved via condensation of two identical 1-acyldipyrromethanes. The statistical synthesis of various meso-substituted porphyrins was achieved via condensation of two non-identical 1-acyldipyrromethanes (Chapter 2).;A new route has been developed for preparing porphyrins bearing up to four different meso-substituents (ABCD-porphyrins). The new strategy relies on two key reactions. One key reaction entails a directed synthesis of a 1-protected 19-acylbilane by acid-catalyzed condensation at high concentration (0.5 M) of a 1-acyldipyrromethane and a 9-protected dipyrromethane-1-carbinol. Three protecting groups were examined, including thiocyanato, ethylthio, and bromo, of which bromo proved most effective. The second key reaction entails a one-flask transformation of the 1-protected 19-acylbilane under the basic Mg-mediated porphyrin-forming conditions. The target magnesium porphyrin is obtained in 65% yield (Chapter 3).;The new route to bilanes and porphyrins bearing four distinct meso substituents has been studied to elucidate the scope and gain entry to previously inaccessible compounds. In total, 19 new porphyrins having alkyl, aryl, heterocylic or no substituent have been synthesized (Chapter 4).;In summary, the basic Mg-mediated conditions provide facile access to novel substituted porphyrins which should facilitate a wide variety of studies.