Synthesis of Chrysoporphyrins and a Related Benzopyrene-Fused System

Abstract

Reaction of 6-nitrochrysene with ethyl isocyanoacetate in the presence of a non-nucleophilic base gave a c-annulated pyrrole ethyl ester that was used to prepare chrysene-fused tripyrranes and a chrysopyrrole dialdehyde. Chrysene-fused tripyrranes were reacted with a pyrrole dialdehyde, but poor yields of chrysoporphyrins were obtained. However, condensation of the chrysopyrrole dialdehyde with a series of tripyrranes afforded excellent yields of chrysoporphyrins and an acenaphtho-chrysoporphyrin. Iron(III) chloride mediated oxidative cyclization of a dihexylchrysoporphyrin afforded a benzopyrene-fused porphyrin that exhibited a strongly red-shifted electronic absorption spectrum. DFT calculations show that both chrysoporphyrins and the benzopyrene-fused porphyrin have tautomers that possess 34π electron delocalization pathways that pass through the porphyrin nucleus and the fused polycyclic aromatic hydrocarbon (PAH) units. Protonation gave dications that favor 36-atom 34π electron circuits. c-Annulated pyrrole dialdehydes were also condensed with a carbatripyrrin to generate PAH-fused carbaporphyrins that retained fully aromatic properties.

Linear Extension of Carbaporphyrin Chromophores: Synthesis, Protonation, and Metalation of Anthro[2,3-b]carbaporphyrins: Evidence for 30π-Electron Aromatic Circuits in a Palladium(II) Complex

“…Tripyrrane dicarboxylic acid 15 (75.2 mg, 0.13 mmol) was stirred with trifluoroacetic acid (1 mL) under nitrogen for 1 min. The mixture was diluted with dichloromethane (50 mL), anthracene dialdehyde 9 (34.3 mg, 0.13 mmol) was immediately added, and the mixture was stirred for 16 h under nitrogen.…”

“…The product fraction was further purified by column chromatography on grade 2 alumina, eluting with 1:1 dichloromethane-hexanes, and the major dark red-brown band was collected. The solvent was removed under reduced pressure, and the residue was recrystallized from (21). Palladium(II) acetate (7.5 mg, 0.045 mmol) was added to a solution of N-methylanthrocarbaporphyrin 111 (8.0 mg, 0.011 mmol) in a 1:1 mixture of acetonitrilechloroform (8 mL), and the solution was stirred for 10 min at room temperature.…”

“…20 In previous studies, the presence of fused aromatic rings greatly reduced the solubility of porphyrin-type structures, but the introduction of long alkyl chains can mitigate this problem. 21 With this in mind, dihexyltripyrrane 15 21 was reacted with dialdehyde 9 in the presence of trifluoroacetic acid (TFA), and following oxidation with 2,3-dichloro-5,6-dicyano-1,4-benzoquinone (DDQ), anthrocarbaporphyrin 8 was isolated in up to 36% yield (Scheme 3). Anthracene-fused carbaporphyrin 8 proved to be reasonably soluble in chloroform, demonstrating that the presence of two long hydrocarbon chains was sufficient to overcome π-stacking interactions due to the anthracene unit.…”

Organometallic Chemistry within the Structured Environment Provided by the Macrocyclic Cores of Carbaporphyrins and Related Systems

“…Carbatripyrrin 37a and oxacarbatripyrrin 37b can be prepared in three steps from technical grade indene. Condensation with pyrrole and furan dialdehydes gave moderate yields of macrocyclic products 38 [ 102 , 103 ] and related carbaporphyrins with fused phenanthrene [ 102 ], acenaphthylene, pyrene and chrysene units [ 104 ] were also obtained. In addition, dioxacarbaporphyrin 39 was generated when dioxocarbatripyrrin 40 was reacted with pyrroledicarbaldehyde 41 [ 105 ].…”

“…Carbaporphyrins retain the porphyrin framework but replace one of the nitrogens with a carbon atom. In early studies, the term “true carbaporphyrins” was introduced [ 22 , 144 ] to differentiate structures such as 102 – 110 ( Figure 5 ) [ 15 , 58 , 67 , 71 , 72 , 102 , 104 ] from other carbaporphyrinoid systems including N-confused porphyrins and azuliporphyrins. This definition includes ring fused structures such as 103 – 110 in much the same way as benzoporphyrin would be considered to be a “true porphyrin” [ 145 , 146 ].…”