Synthesis of 2‐Arylpyrimido[4,5‐b]porphyrins via Cyclization Reaction with Ammonia

Abstract

A facile synthetic strategy for the synthesis of a new series of β,β’‐fused 2‐arylpyrimido[4,5‐b]porphyrins has been developed by using condensation cyclization reaction with ammonia. 2‐Aroylamino‐3‐formylporphyrins were synthesized from 2‐aroylaminoporphyrins under Vilsmeier–Haack reaction conditions, which were then efficiently converted to the corresponding 2‐arylpyrimido[4,5‐b]‐5,10,15,20‐tetrakis(4‐chlorophenyl)‐porphyrins via a condensation cyclization reaction. The nickel(II), copper(II), free‐base and zinc(II) analogues of 2‐arylpyrimido[4,5‐b]porphyrins were successfully synthesized in 65–72 % yields and structurally characterized on the basis of spectral data analysis. On photophysical evaluation, 2‐arylpyrimido[4,5‐b]porphyrins demonstrated a 12–19 nm bathochromic shift in their electronic absorption spectra and up to 10 nm red shift in their emission spectra as compared to the simple meso‐(tetrakis(4‐chlorophenyl))porphyrins due to the extended π‐conjugation.

Cascade Radical Pathway-Enabled Nitrogen–Sulfur Coupling: Access to Isothiazolo[3,4-b]-meso-tetraarylporphyrins

“…The synthesis of nickel­(II) and copper­(II) isothiazolo­[3,4- b ]-5,10,15,20-tetraarylporphyrins ( 3a–f ) began with the preparation of nickel­(II) and copper­(II) 2-benzoylamino-3-formyl-5,10,15,20-tetraarylporphyrins ( 2a–f ) as building blocks from 2-benzoylamino-5,10,15,20-tetraarylporphyrins ( 1a–f ) using freshly prepared chloroiminium ions, generated in situ by adding N , N -dimethylformamide (DMF) in phosphorus oxychloride (POCl 3 ), under Vilsmeier–Haack reaction conditions (Scheme ). After chromatographic purification and structural characterization of porphyrins ( 2a–f ), a model reaction was carried out by taking nickel­(II) 2-benzoylamino-3-formyl-5,10,15,20-tetraphenylporphyrin ( 2a ) as a model substrate for the synthesis of nickel­(II) isothiazolo­[3,4- b ]-5,10,15,20-tetraphenylporphyrin ( 3a ). Various solvents were screened at different temperatures, and the most favorable outcome with 55% yield of porphyrin ( 3a ) was achieved by employing toluene as a solvent and Lawesson’s reagent at 110 °C as presented in Table S1 (see the Supporting Information).…”

“…Purple solid; yield: 87 mg (59%); UV (CHCl 3 ) λ max (ε × 10 −4 M −1 cm −1 ): 438 (20.86), 551 (1.20) Nickel(II) 2-Benzoylamino-3-formyl-5,10,15,20-tetrakis(4chlorophenyl)porphyrin (2b). 25 Purple solid; yield: 94 mg (55%); UV (CHCl 3 ) λ max (ε × 10 General Procedure for the Synthesis of Nickel(II) and Copper(II) Isothiazolo[3,4-b]-5,10,15,20-tetraarylporphyrins (3a−f). To a stirred solution of nickel(II) or copper(II) 2benzoylamino-3-formyl-5,10,15,20-tetraarylporphyrins (2a−f, 0.024 mmol) in toluene (5 mL) was added Lawesson's reagent (19.4 mg, 0.048 mmol).…”

“…Besides, various porphyrin derivatives have demonstrated their ability to play vital roles in photoredox catalysis, reversible proteasome inhibitors, donor–acceptor biomorphs, sonosensitizer for periodontitis sonodynamic therapy, and C–H bond activation . Moreover, these macrocycles are suitable constituents for constructing the dye-sensitized solar cells and supramolecular frameworks due to their exceptional characteristics such as rigid and flat molecular structure, high thermal stability, strong absorption and emission of light, and a narrow energy gap between their highest occupied molecular orbital and lowest unoccupied molecular orbital. , Hence, a wide range of synthetic strategies were devised to construct diverse β- and meso -functionalized porphyrinic systems through peripheral modifications in previous years. − Additionally, porphyrins fused with imidazole and triazole ring systems have shown their importance as fundamental building blocks for multiporphyrinic arrays and oligomers that exhibited enhanced electronic properties. , On the other hand, isothiazole, another class of five-membered heterocycles present as a pharmacophore in many biologically active compounds, displayed a wide range of pharmaceutical profiles such as anticancer, antidiabetic, anti-Alzheimer, anticonvulsive, and antithrombotic activity . Furthermore, isothiazole-embedded molecules have also shown lower band gaps and thereby found to be beneficial for organic solar cell applications .…”

A divergent one-pot thiol-Michael strategy to create β-thiophene-fused porphyrins

“…10 a,b During the past decades, a large number of periphery modified π-extended porphyrins have been constructed by using meso -tetraarylporphyrins as easily accessible building blocks. 11–27,28 a–d Some of these macrocycles have been explored as light-harvesting materials in organic solar cells due to their strong light absorption properties. 29 Similarly, thiophene-fused aromatic systems have demonstrated their potential usage in organic semiconductors, 30 microelectronics, 31 electroluminescent materials, 32 conducting polymers 33 and solar cells.…”