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.

An alternative synthesis of benziporphyrins starting from isophthaloyl chloride

“…13 8,9,13,14,18,19-Hexamethylbenziporphyrin (20). Benzitripyrrane diethyl ester 17 (100 mg, 0.215 mmol) was refluxed with sodium hydroxide (40 mg) in ethylene glycol under nitrogen for 1 h. The mixture was cooled to room temperature, diluted with water, and extracted with hexanes.…”

“…Selected EI-MS, 1 H NMR, 1 H-1 H COSY, HSQC, DEPT-135, 13 C NMR, and UV-Vis spectra are provided as supplementary materials. This material is available free of change via the Internet at http://worldscinet.com/ jpp/jpp.shtml.…”

“…This results in cross-conjugated structures that are devoid of macrocyclic aromatic properties [8]. However, electron-donating substituents such as methoxy groups introduce a degree of diatropic character [9] and protonated benziporphyrins also appear to possess significant diamagnetic ring currents [9][10][11][12][13][14][15]. Benziporphyrins act as dianionic organometallic ligands, forming stable derivatives with Ni(II), Pd(II), Pt(II), etc.…”

“…Benziporphyrins act as dianionic organometallic ligands, forming stable derivatives with Ni(II), Pd(II), Pt(II), etc. [13][14][15][16][17][18][19][20]. In addition, meso-tetraarylbenziporphyrins undergo selective oxidation reactions with silver(I) acetate [12,17], and rhodium(III) derivatives can undergo ring contraction reactions to afford metalated carbaporphyrins [21].…”

“…Alternatively, benzene dicarbinols 6 react with 3 equivalents of pyrrole and 2 equivalents of an aromatic dialdehyde in the presence of boron trifluoride etherate to give meso-tetraarylbenziporphyrins 7 (Scheme 1) [11,17]. These strategies have been adapted for the synthesis of heterobenziporphyrins [13,15], naphthiporphyrins [14] and fully aromatic oxybenzi porphyrins [10,14,24,25]. In order to further extend our inquiries into these types of porphyrinoid analogs, we have investigated the development of new synthetic routes to benziporphyrins and related systems.…”