Palladium-catalyzed meso-amination and amidation of porphyrins: marked acceleration with the Ni(II) central metal ion

The preparation of meso-amino and meso-amido substituted porphyrins was easily accomplished by palladium-mediated cross-coupling reactions of meso-brominated porphyrins with amines and amides. Ni(II) introduced as a central metal ion into the substrate porphyrin markedly accelerated the cross-coupling.     

Enhancement of phlorin stability by the incorporation of meso-mesityl substituents

The effect of sterically bulky mesityl substituents on the stability of meso-substituted phlorins was examined. Three different phlorins bearing zero, two or three mesityl substituents were prepared via alkylation of the appropriate porphyrins. The stability of each phlorin was examined by UV-vis spectral monitoring of dilute solutions exposed to ambient light and air. UV-vis and mass spectral analyses performed after decomposition revealed qualitative differences in the degradation products. This study shows that the selection and positioning of peripheral substituents can enhance phlorin stability.     

Synthesis of meso-furyl porphyrins with N4, N3S, N2S2 and N3O porphyrin cores

A series of meso-furyl porphyrins with four different porphyrin cores (N₄, N₃S, N₂S₂ and N₃O) were synthesized and characterized. The comparison of NMR, optical and fluorescence properties of meso-furyl porphyrins with porphyrins with six-membered aryl groups indicates that electronic properties of porphyrins were changed drastically on the introduction of furyl groups at meso positions. The maximum shifts in spectral bands were observed for meso-furyl porphyrins with N₂S₂ core. On protonation, the absorption bands of meso-furyl porphyrins were further red shifted. All these changes were ascribed to the possibility of more planarity of the meso-furyl porphyrins due to the small size of the furyl groups which results in extending the π-delocalisation of the porphyrin ring in to the furyl groups.     

Convergent synthesis of meso-ferrocenyl porphyrins for TiO2 sensitization

Electron-donating ferrocenyl moieties have been incorporated into supramolecular carboxyporphyrin architectures Zn(II)-5-ferrocenyl-10,20-bistolyl-15-(4-methylbenzoate)porphyrin (trans-Fc-ZnP-CO₂Me), Zn(II)-5-ferrocenyl-10,15,20-tris(4-methylbenzoate)porphyrin [trans-Fc-ZnP-(CO₂Me)₃], and Zn(II)-5,15-bisferrocenyl-10,20-bis(4-benzoate)porphyrin [trans-Fc₂-ZnP-(CO₂Me)₂] for self-assembly on metal oxide nanoparticles. Efficient and economic synthesis has required a convergent strategy toward reduced symmetry trans-A₂B₂ and trans-AB₂C substitution patterns about the porphyrin macrocycle minimizing the production of porphyrin side products and increasing yields of the target ferrocenylporphyrins. Preliminary spectroscopic data in solution and in the solid state bound to mesoporous TiO₂ films are discussed.     

Synthesis of meso-tetraphenyl porphyrins via condensation of dipyrromethanes with N-tosyl imines

A new synthetic route for the synthesis of 5,10,15,20-tetraphenyl porphyrins has been developed based on the reaction of 5-substituted dipyrromethanes with N-tosyl imines in the presence of a metal triflate catalyst. meso-Substituted tetraphenyl porphyrins were synthesized in a two-step process. The first step of the method is the metal triflate-catalyzed condensation of 5-substituted dipyrromethanes with N-tosyl imines to form a porphyrinogen intermediate and the second step is the oxidation of the porphyrinogen to porphyrin. The method was applied to the synthesis of trans-A₂B₂-tetraarylporphyrins and the products were obtained with only a trace amount of one scrambling product. The synthesis of two important building blocks for porphyrin synthesis, mono and di-sulfonamide alkylated 5-substituted dipyrromethanes, was achieved by the addition of 5-substituted dipyrromethane to N-tosyl imine. The application of mono and di-sulfonamide alkylated 5-substituted dipyrromethanes in ‘2+2’ porphyrin formation reactions is presented.     

Synthesis of mono meso-pyridyl 21,23-dithiaporphyrins and unsymmetrical non-covalent porphyrin dimers

A new method has been developed to synthesize 21,23-dithiaporphyrins having one pyridyl group at the meso position. The method required easily available unknown precursors and the condensation resulted in mono meso-pyridyl 21,23-dithiaporphyrins as single products in 8-11% yield. Two of the three mono meso-pyridyl N₂S₂ porphyrins were used to synthesize non-covalent unsymmetrical porphyrin dimers containing one N₂S₂ and one N₄ porphyrin cores.     

An unprecedented regioselective lithiation of dipyrromethanes. Synthesis of meso-functionalized dipyrromethanes

Functionalization of meso-positions of dipyrromethanes, gives valuable intermediates through a highly regioselective lithiation-substitution sequence.     

Ring size selective synthesis of meso-aryl expanded porphyrins

meso-Aryl expanded porphyrins were prepared in a ring size selective manner from methanesulfonic acid-catalyzed reaction of dipyrromethane and tripyrromethane with aryl aldehydes.     

Asymmetric synthesis of 3,4-dihydroxyglutamic acids via enantioselective reduction of cyclic meso-imide

Stereoselective synthesis of (3S,4S)- and (3R,4R)-series of 3,4-dihydroxyglutamic acids was investigated. The key reaction in this synthesis is asymmetric reduction of meso-imide derived from meso-tartaric acid. Lewis acid-promoted cyanation of the obtained optically active lactam via the acyliminium intermediate followed by standard deprotection procedure afforded the desired 3,4-dihydroxyglutamic acids.     

Synthesis of highly substituted meso-tetraarylporphyrins

meso-Tetraphenylporphyrin (and its derivatives), in the reaction with fuming yellow nitric acid (d=1.53), form either 5-(4-nitroaryl)-10,15,20-triarylporphyrin, 5,10-bis(4-nitroaryl)-15,20-diarylporphyrin, or 5,10,15-tris(4-nitroaryl)-20-arylporphyrin, depending on the reaction temperature (0-20 °C), amounts of the acid used, and reaction time. The above nitroporphyrins react, in the presence of a base (t-BuOK) at 0 °C, with carbanions (which bear nucleophugal groups at the carbanionic center: ⁻CH(Cl)SO₂Tol, ⁻CH(Br)SO₂Tol, and ⁻CH(Cl)SO₂NMe₂), leading to the nucleophilic substitution of hydrogen in one or more of the meso-nitroaryl rings. By this route, the preparation of the highly substituted ‘synthetic’ porphyrins (bearing up to ten O-, N-, Cl-, or C-substituents) was demonstrated.     

1,9-Bis(N,N-dimethylaminomethyl)dipyrromethanes in the synthesis of porphyrins bearing one or two meso substituents

A synthesis of 5,15-disubstituted zinc-porphyrins has been developed that employs condensation of a 1,9-bis(N,N-dimethylaminomethyl)dipyrromethane+a dipyrromethane in refluxing ethanol containing zinc acetate followed by oxidation with DDQ. The N,N-dimethylaminomethylation of the dipyrromethane was achieved via Eschenmoser's reagent (N,N-dimethylmethyleneammonium iodide) in CH₂Cl₂ at room temperature. The synthesis is compatible with diverse substituents (e.g., alkyl, aryl, ester, acetal) and enables rapid synthesis of trans-AB-, A₂-, and A-porphyrins. The synthesis of >40 zinc porphyrins has been surveyed; 13 zinc porphyrins were isolated in yields of 5-20% without detectable scrambling.     

Synthesis and characterizations of meso-disubstituted asymmetric porphycenes

A post-synthetic method has been developed to synthesize novel asymmetric porphycenes bearing two different substituents on the meso-positions. Nitration of 9-acetoxy-2,7,12,17-tetra-n-propylporphycene with AgNO₃ in CH₃COOH/CH₂Cl₂ occurs regioselectively at the 19-position of the macrocycle to give 9-acetoxy-19-nitro-2,7,12,17-tetra-n-propylporphycene (3a) which was readily converted to 9-acetoxy-19-amino-2,7,12,17-tetra-n-propylporphycene (4a) by the reduction with SnCl₂ in pyridine.     

Asymmetric desymmetrization of meso-vic-diols by carbamoylation catalyzed with a chiral Cu(II) complex

Asymmetric desymmetrization of meso-vic-diols was achieved by carbamoylation in the presence of copper triflate and (S,S)-Ph-BOX as a catalyst without any use of bases. The method was successfully applied to asymmetric desymmetrization of five- to eight-membered cyclic meso-vic-diols in high enantioselectivity with up to 93% ee.     

Facile synthesis of meso-substituted dipyrromethanes and porphyrins using cation exchange resins

The macroporosity and acidity of cation exchange resins play a crucial role in the synthesis of dipyrromethanes and porphyrins; for the first time, cation exchange resins have been used as heterogeneous solid acid catalysts to produce dipyrromethanes and porphyrins in good yields. The reaction, at room temperature, of substituted aromatic aldehydes with pyrrole catalysed by cation exchange resin afforded the corresponding meso-substituted dipyrromethane in yields ranging from 70 to 80%, indicating the broad scope of the reaction. Further, the condensation of meso-substituted dipyrromethane with similar or different substituted aromatic aldehydes, using cation exchange resins furnished meso-tetrakis-symmetrical and mixed porphyrins, respectively. One-pot synthesis of porphyrins can also be carried out directly from the aldehydes and pyrrole under the above conditions. Acidolysis of the dipyrromethane is negligible under the conditions of the porphyrin-forming reaction.     

Copper-catalysed meso-bislactone ring opening using Grignard and mixed triorganozinc reagents

An efficient copper-mediated S_N2′ ring-opening reaction of a meso-bislactone has been developed using Grignard reagents and, for the first time, mixed triorganozinc reagents.     

Copper complex catalyzed asymmetric monosulfonylation of meso-vic-diols

Asymmetric desymmetrization of meso-vic-diols was performed by tosylation in the presence of copper(II) triflate and (R,R)-Ph-BOX as a catalyst. The method was successfully applied to asymmetric desymmetrization of cyclic and acyclic meso-vic-diols in high enantioselectivity with up to >99% ee.     

Highly regioselective lithiation of inter-ring carbon of bis(thien-2yl)methane: a general meso-elaboration protocol

Bis(thien-2yl)methane is regioselectively lithiated at the inter-ring methylene carbon using dimsyl anion in THF at 0 °C; quenching with appropriate electrophile furnishes meso-elaborated derivatives, exclusively with synthetic advantage.     

An imino-Diels-Alder route to meso-2,6-disubstituted-4-piperidones

A convenient stereoselective preparation of meso-2,6-disubstituted-4-piperidones has been developed by imino-Diels-Alder reaction of 2-amino-1,3-butadienes with imines in the presence of catalytic amount of Cu(TfO)₂.     

Synthesis of meso-tetraarylporphyrins using SeO2 as oxidant

The oxidative step of the two-step, one-flask synthesis of meso-tetraarylporphyrins is herein conducted with heterogeneous oxidant SeO₂ instead of the usual quinones DDQ or p-chloranil. Evaluation of BF₃O(Et)₂ or I₂ amount for the condensation of the first step combined with the excess of SeO₂ defined porphyrin synthesis conditions employing benzaldehydes and pyrrole (or 5-phenyldipyrromethane) as starting materials. The simplicity of the workup, allied with reaction mild conditions, makes this method a good option for the synthesis of this kind of compound.     

Radical mediated stereoselective synthesis of meso-7,11-dimethylheptadecane, a female sex pheromone component of the spring hemlock looper and the pitch pine looper

meso-7,11-Dimethylheptadecane, a female sex pheromone component of the spring hemlock looper and the pitch pine looper, was synthesized from ethyl 2-(bromomethyl)propenoate in nine steps and 14% overall yield. The key step in the synthesis is the highly diastereoselective chelation-controlled radical reaction of diethyl 4-benzyloxy-2,6-dimethyleneheptanedioate with pentyl iodide performed in the presence of 6 equiv of MgBr₂·OEt₂.