A novel method for the synthesis of dipyrromethanes by metal triflate catalysis

5-Substituted dipyrromethanes were synthesized by the reaction of N-tosyl imines with excess pyrrole in the presence of metal triflates. Tripyrromethane and other oligomeric side products were not observed. High yields of 5-substituted dipyrromethanes were obtained for electron donating and withdrawing substituents by performing the reaction at two different temperatures. The new reaction procedure is simple and anhydrous conditions are not required.     

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.     

Synthesis of substituted salicylamines and dihydro-2H-1,3-benzoxazines

Phenols were converted to their magnesium salts with the MgCl₂-Et₃N base system and subsequently reacted with Eschenmoser's salt, affording N,N-dimethyl substituted benzylamines in high to excellent yields. A series of mono N-substituted benzylamines were prepared in one-pot syntheses by ortho-formylation of phenols to corresponding salicylaldehydes, which in turn reacted with amines to imines. The imines were subsequently reduced to mono N-substituted benzylamines. Some of these benzylamines were further converted, without work-up, to mono N-substituted dihydro-2H-1,3-benzoxazines.     

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.     

Highly stereoselective aziridination of imines with (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide

Addition of (S)-dimethylsulfonium-(p-tolylsulfinyl)methylide to N-tosyl imines afforded the corresponding sulfinyl aziridines with full enantio- and diastereoselectivity. The chiral sulfinyl substituent was removed without ring opening leading to enantiopure 2-substituted aziridines.     

Regioselective addition of pyrrole to N-tosyl imines in the presence of Cu(OTf)2

The Cu(OTf)₂ catalysed reaction of pyrrole with N-tosyl imines gives pyrrole sulfonamides in high yields. The addition reaction takes place regioselectively at C(2) of the pyrrole. The procedure is simple and does not require anhydrous conditions.     

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.     

The reaction of N-tosyl imines with heteroaromatic compounds: a new access to triheteroarylmethanes

Useful triheteroarylmethanes were prepared by the double Friedel-Crafts reaction of a wide variety of aromatic N-tosyl imines with furan, thiophene, and pyrrole in the presence of Cu(OTf)₂ and Montmorillonite K-10 clay catalysts.     

Efficient and versatile single pot approach to dipyrromethanes and bis(heterocyclyl)methanes

An efficient single pot route is presented involving the use of O, N-perhydro 1,3-heterocycles as carbonyl equivalents for the synthesis of 5-substituted dipyrromethanes, 5,10-disubstituted tripyrranes and bis(heterocyclyl)methanes.     

Concise and diastereoselective approach to syn- and anti-N-tosyl-α-hydroxy β-amino acid derivatives

The methyl diazoacetate and aryl (N-tosyl)imines can be transformed into syn or anti α-hydroxy β-amino esters with high diastereoselectivities in three steps: the base promoted nucleophilic condensation of the methyl diazoacetate and aryl (N-tosyl)imines to give β-(N-tosyl)amino α-diazoesters, followed by oxidation with Oxone^® to generate α-oxo esters, which were reduced with NaBH₄ to yield the anti-N-tosyl-α-hydroxy β-amino ester, or hydrogenated with Pd/C (10%) as the catalyst to yield corresponding syn isomer, both in high diastereoselectivity.     

The Diels–Alder reactions of para-benzoquinone nitrogen-derivatives: an experimental and theoretical study

An experimental and theoretical study of the comparative reactivity and selectivity of the Diels–Alder reactions of para-benzoquinones and three nitrogen derivatives have been performed. The mono-oximes derivatives do not react under the tested reaction conditions, whereas the tosylated mono-oximes react slowly. However, the mono N-tosyl imines show excellent reactivity, and superior to the parent para-benzoquinones. DFT calculations support these experimental results.     

Synthesis and fluorescence properties of covalently linked homo- and hetero-porphyrin dyads containing meso-tolyl porphyrin and meso-furyl porphyrin sub-units

Three porphyrin building blocks with N₄, N₃S and N₂S₂ cores having three meso-furyl groups and one meso-iodophenyl group were synthesized and characterized. The porphyrin building blocks were used to synthesize six porphyrin dyads such as N₄-N₄, N₃S-N₃S, N₂S₂-N₂S₂, N₄-N₃S, N₄-N₂S₂ and N₃S-N₂S₂ containing meso-tolyl and meso-furyl porphyrin sub-units under mild Pd(0) mediated coupling conditions. Steady state fluorescence studies indicated an efficient energy transfer from the meso-tolyl porphyrin sub-unit to the meso-furyl porphyrin sub-unit in all six dyads. This study supported the argument that the meso-furyl porphyrins can be used as good energy acceptors when meso-aryl porphyrins act as energy donors in their metal free form.     

Simple route to meso-substituted trans-A2B2-porphyrins bearing pyridyl units

We have developed a methodology that affords regioisomerically pure trans-A₂B₂-porphyrins bearing pyridyl substituents. The optimal conditions for their synthesis were identified by the modification of known conditions for the reaction of dipyrromethanes with aromatic aldehydes. A total of five new porphyrins were synthesized.     

Stereoselective synthesis of N-heterocycles: application of the asymmetric Cu-catalyzed addition of Et2Zn to functionalized alkyl and aryl imines

The preparation of N-heterocycles from alkyl- and aryl-substituted imines is described. The key step involves a copper-catalyzed addition of diethylzinc to functionalized alkyl-substituted imines that were generated in situ from the sulfinic acid adducts. The nucleophilic addition products were then converted to 2-substituted pyrrolidines and piperidines. Aryl-substituted imines were transformed into enantioenriched 1- and 1,4-substituted tetrahydroisoquinolines.     

Asymmetric synthesis of a 3,4-substituted pyrrolidine by l-proline catalyzed direct enolexo aldolization

The asymmetric synthesis of a 3,4-substituted N-tosyl pyrrolidine has been achieved by using l-proline catalyzed 5-enolexo aldolization with high enantio and diastereoselectivity.     

meso-Multi(iodophenyl) porphyrins: synthesis, isolation, and identification

We report on a simple method for identification of a series of six meso-substituted porphyrins by ¹H NMR spectroscopy. The meso-substituted porphyrins are synthesized by a simple mixed-aldehyde condensation approach [3,5-di-tert-butylstyrylbenzaldehyde (A) and 4-iodobenzaldehyde (B)] to give the two parent porphyrins (A₄, B₄) and four hybrid porphyrins (A₃B, cis-A₂B₂, trans-A₂B₂, AB₃) which are isolated and characterized.     

Chiral N-phosphonyl imine chemistry: new reagents and their applications for asymmetric reactions

Novel chiral N-phosphonyl imines 2 have been designed and synthesized using chiral N-phosphoramide 1. These N-phosphonyl imines have been successfully utilized for asymmetric aza-Darzens reaction and asymmetric aza-Henry reaction. The C₂-symmetric chiral auxiliary tolerates oxidation, is not sensitive to racemization and can be recycled for large scale synthesis.     

Alkynylation of N-tosylimines with aryl acetylenes promoted by ZnBr2 and N,N-diisopropylethylamine in acetonitrile

We found a suitable condition for the effective alkynylation of N-tosylimines with aryl acetylenes. The reaction of N-tosylimines and aryl acetylenes in the presence of ZnBr₂ and DIEA (N,N-diisopropylethylamine) in CH₃CN afforded the desired N-tosyl propargylamines in moderate to good yields.     

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.     

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.