| Abstract
| - Porphyrins bearing specific patterns of substituents are crucial building blocks in biomimetic andmaterials chemistry. We have developed methodology that avoids statistical reactions, employsminimal chromatography, and affords up to gram quantities of regioisomerically pure porphyrinsbearing predesignated patterns of up to four different meso substituents. The methodology is basedupon the availability of multigram quantities of dipyrromethanes. A procedure for the diacylationof dipyrromethanes using EtMgBr and an acid chloride has been refined. A new procedure for thepreparation of unsymmetrical diacyl dipyrromethanes has been developed that involves (1)monoacylation with EtMgBr and a pyridyl benzothioate followed by (2) introduction of the secondacyl unit upon reaction with EtMgBr and an acid chloride. The scope of these acylation methodshas been examined by preparing multigram quantities of diacyl dipyrromethanes bearing a varietyof substituents. Reduction of the diacyl dipyrromethane to the corresponding dipyrromethane-dicarbinol is achieved with NaBH4 in methanolic THF. Porphyrin formation involves the acid-catalyzed condensation of a dipyrromethane-dicarbinol and a dipyrromethane followed by oxidationwith DDQ. Optimal conditions for the condensation were identified after examining various reactionparameters (solvent, temperature, acid, concentration, time). The conditions identified (2.5 mMreactants in acetonitrile containing 30 mM TFA at room temperature for <7 min) provided reactionwithout detectable scrambling (LD-MS) for aryl-substituted dipyrromethanes, and trace scramblingfor alkyl-substituted dipyrromethanes. The desired porphyrins were obtained in 14−40% yield.The synthesis is compatible with diverse functionalities: amide, aldehyde, carboxylic acid, ester,nitrile, ether, bromo, iodo, ethyne, TMS-ethyne, TIPS-ethyne, perfluoroarene. In total 30 porphyrinsof the types A3B, trans-A2B2, trans-AB2C, cis-A2B2, cis-A2BC, and ABCD were prepared, including>1-g quantities of three porphyrins.
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