New One-Step Synthesis of 3,4-Disubstituted Pyrrole-2,5-dicarbaldehydes

An alternative route to benziporphyrins has been developed. Reaction of an α-unsubstituted pyrrole ethyl ester with isophthaloyl chloride in the presence of aluminum chloride afforded a diketone that underwent selective reduction with diborane to give a benzitripyrrane. Cleavage of the ethyl esters with sodium hydroxide in refluxing ethylene glycol, followed by acid catalyzed condensation with a pyrrole dialdehyde and oxidation with DDQ, generated the targeted benziporphyrin product. Spectrophotometric titration of the benziporphyrin with trifluoroacetic acid (TFA) demonstrated the sequential formation of mono-and dicationic species. At lower dilutions, the free base benziporphyrin showed unusually strong 5 J HH coupling between two adjacent methyl substituents, indicating that the connecting unit has substantial olefinic characteristics.

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“…The deprotected benzitripyrrane was dissolved in dichloromethane, 3,4-dimethylpyrrole-2,5-dicarbaldehyde [27,28] …”

Section: Methodsmentioning

confidence: 99%

An alternative synthesis of benziporphyrins starting from isophthaloyl chloride

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2017

J. Porphyrins Phthalocyanines

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“… 6 Corroles tend to break to open-chain structures in aerobic solution under ambient light. 8 Free-base corroles are unstable against light and air due to the reduced aromaticity and nonplanarity of the macrocycle. The stability depends on the substitution pattern of the tetrapyrrolic macrocycle and is improved by electronegative substituents.…”

mentioning

confidence: 99%

Spectroscopic Scanning Tunneling Microscopy Studies of Single Surface-Supported Free-Base Corroles

et al. 2011

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Corroles are versatile chemically active agents in solution. Expanding their applications toward surface-supported systems requires a fundamental knowledge of corrole–surface interactions. We employed the tip of a low-temperature scanning tunneling microscope as local probe to investigate at the single-molecule level the electronic and geometric properties of surface-supported free-base corrole molecules. To provide a suitable reference for other corrole-based systems on surfaces, we chose the archetypal 5,10,15-tris(pentafluorophenyl)corrole [H3(TpFPC)] as model system, weakly adsorbed on two surfaces with different interaction strengths. We demonstrate the nondissociative adsorption of H3(TpFPC) on pristine Au(111) and on an intermediate organic layer that provides sufficient electronic decoupling to investigate geometric and frontier orbital electronic properties of almost undisturbed H3(TpFPC) molecules at the submolecular level. We identify a deviating adsorption behavior of H3(TpFPC) compared to structurally similar porphyrins, characterized by a chiral pair of molecule–substrate configurations.

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“…In 1998, Tardieux and co-workers presented a simple and mild one-step route for the synthesis of 3,4-disubstituted pyrrole-2,5dicarbaldehydes (372) via the diformylation 346,347 reaction of bsubstituted pyrrole-2-carboxylic acids (371) with TEOF (5) in triuoroacetic acid, in a dual role of catalyst and solvent, at room temperature for 1 h in 22-65% yields (Scheme 105). 347 Tri-(pyrrol-2-yl)alkanes (374) could be synthesized via the reaction of pyrrole (373) with orthoesters (5, 7, 62, 102) using chloroacetic acid (45 mmol) in CH 2 Cl 2 at 0 C within 30 min, in 34-38% yields (Scheme 106). 5-Phenyl-4,6-dipyrrin has also been prepared in comparatively good yield (51%) through the reaction of pyrrole with trimethyl orthobenzoate by dichloroacetic acid (38 mmol) under similar conditions.…”

Section: Synthesis Of Pyrrole Derivativesmentioning

confidence: 99%