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[摘要]：27 New methodol. is described for the synthesis of porphyrins bearing four (A4, cis-A2B2, cis-ABC2, trans-A2B2) or fewer (A, cis-AB, cis-A2, trans-A2) meso substituents. The method entails condensation of two 1-acyldipyrromethanes in the presence of a metal salt (MgBr2, 3 mol equiv) and a noncoordinating base (DBU, 10 mol equiv) in a noncoordinating solvent (toluene) with heating (conventional or microwave irradn.) and exposure to air. 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. Both routes possess attractive features including (1) no scrambling, (2) good yield (up to reasonable scope (aryl, heteroaryl, alkyl, or no substituent), (4) short reaction time (~2 h) via microwave irradn., (5) magnesium porphyrins as the products, which easily undergo demetalation, and (6) facile chromatog. purifn. A key advantage of the statistical route is to obtain a cis-substituted porphyrin without the corresponding trans isomer. For example, reaction of an A/B-substituted 1-acyldipyrromethane and the fully unsubstituted 1-formyldipyrromethane gave the magnesium chelates of three porphyrins: the trans-A2B2-porphyrin, the hybrid cis-AB-porphyrin, and porphine (no trans-AB-porphyrin can form), which were readily demetalated and sepd. as the free base species. Altogether 26 1-acyldipyrromethanes and 26 target porphyrins were prepd., including many with two different pyridyl substituents. One set of amphipathic porphyrins includes cis-A2B2- or cis-A2BC-porphyrins wherein A = pentyl and B/C = pyridyl (o-, m-, p-). Taken together, the rational and statistical routes enable facile conversion of readily available 1-acyldipyrromethanes to diverse porphyrins bearing 1-4 meso substituents for which access is limited via other methods. |
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