RATIONAL TETRAARYLPORPHYRIN SYNTHESES - TETRAARYLPORPHYRINS FROM THE MACDONALD ROUTE

Four new synthetic routes to meso-tetraarylporphyrins using a MacDonal d-type 2 + 2 condensation are described. Self-condensation of a 5-aryl dipyrromethane (e.g., 17) with an aryl-substituted one-carbon bridging unit affords a mixture of tetraarylporphyrins due to acid-catalyzed r edistribution reactions. The second and third methods presented here s how wide applicability for the preparation of 5,10,15,20-tetraaryl-sub stituted porphyrins (e.g., 31, 37, 48, 49) with 2-fold rotational symm etry and involve self-condensation of 5-aryl-1-aryldipyrromethanecarbi nols. Finally, the fourth approach involves a 2 + 2 approach in which one of the two dipyrromethanes bears both of the bridging carbons in t he porphyrin products, affording porphyrin 50 which possesses three di fferent aryl rings, with one pair of uniquely opposite identical aryl groups. The last two 2 + 2 methods are further extended to give a tetr aarylporphyrin 38 bearing four different aryl groups in a predesignate d array, the structure of which is confirmed by a single-crystal X-ray study.