Synthesis and metalation of dimethoxybenziporphyrins, thiabenziporphyrins, and dibenziporphyrins.

Abstract

Dimethoxybenzitripyrranes were prepared in excellent yields by reacting benzene dicarbinols with BF3·Et2O and excess pyrrole in refluxing 1,2-dichloroethane. Reaction with a pyrrole dialdehyde in the presence of TFA, followed by oxidation with DDQ, afforded good yields of meso-diphenyldimethoxybenziporphyrins. These dimethoxyporphyrinoids exhibited weakly diatropic properties that were enhanced upon protonation. The dimethoxybenzitripyrranes also reacted with a thiophene dicarbinol to give dimethoxythiabenziporphyrins, and the nonplanar nature of this system was demonstrated by X-ray crystallography. The dimethoxybenziporphyrins reacted with palladium(II) acetate to give the related organometallic derivatives, but the thiabenziporphyrins underwent a demethylation to afford palladium(II) thiaoxybenziporphyrins. Related palladium(II) complexes were also prepared from previously reported thiacarbaporphyrinoids. The X-ray structure for one of the complexes showed that the six-membered ring is very distorted and the thiophene ring is strongly tilted out of the plane of the macrocycle. The dimethoxybenzitripyrranes also reacted with dimethoxybenzene dicarbinols to give the first examples of dibenziporphyrins, thereby further demonstrating the versatility of this synthetic methodology.