One Carbon Ring Expansion of Bipyrrole to Bipyridine Enables Access to a π-Extended, Non-innocent, Corrole-like Ligand.

A π-extended, diaza-triphenylene embedded, mono-anionic corrole analogue and its NiII complex were synthesized from a diaza-triphenylene precursor, which was obtained from a double one-carbon insertion into a naphthobipyrrole diester. Following conversion to the corresponding activated diol and acid-catalyzed condensation with pyrrole, subsequent reaction with pentafluorobenzaldehyde afforded mono-anionic, π-extended bipyricorrole-like macrocycle. Attempted NiII insertion with Ni(OAc)2 ⋅ 4H2 O resulted an ESR active, NiII bipyricorrole radical complex, which was converted to a stable cationic NiII complex upon treatment with [(Et3 O)+ (SbCl6 )- ]. Both complexes were characterized by 1 H and 13 C NMR, UV/Vis spectroscopy and single crystal X-ray diffraction analysis. The NiII bipyricorrole radical complex is converted to a cationic NiII complex by single-electron reduction using cobaltocene. Both the cationic NiII complex and the radical NiII complex exhibited ligand-centered redox behavior, whereas the NiII remains in the +2 oxidation state.

Synthesis, photophysical properties and photo-induced cytotoxicity of novel tris(diazatriphenylene)ruthenium (II) complex.

Novel bipyridine-based heterocyclic building block, 3,10-dichloro-benzo[f][1,10]phenanthroline and its Ruthenium(II) complex have been synthesized and fully characterized. The synthesized Ru(II)-complex is highly luminescent displaying emission at 590 nm with quantum yield of ∼0.8 in methanol. Ru(II) complex showed photocytotoxicity upon 400 nm blue light irradiation. Mechanistic study revealed that photoactivated Ru(II) complex generates reactive radical species which can damage the protein inside the cells and induce cell death even with short irradiation time.

meso-Bis(ethynyl) Versus meso-Bis(aryl) Calix[4]pyrroles: Dimensionally Well-Modulated Receptors That Can Regulate the Anion Binding Domains.

meso-Substituted calix[4]pyrroles 2-6 containing a direct meso-ethynyl linker displayed high binding affinities and unique conformational features on halide anion binding. A general conformational bias for the equatorial alignments of the meso-(aryl)ethynyl groups was observed in the host-halide complexes which was attributed to the repulsive anion-alkyne interactions and released steric strain. Such conformational features of host-halide complexes persisted even in the case of calix[4]pyrrole 6 bearing cationic meso components, which displayed the highest binding affinity for chloride anions among known meso-aryl calix[4]pyrroles. Synthetic details, conformational features, and comparative halide anion binding properties of this series of calix[4]pyrroles are described.

Multicomponent dipolar cycloadditions: efficient synthesis of polycyclic fused pyrrolizidines via azomethine ylides.

An efficient multicomponent dipolar cycloaddition for the synthesis of polycyclic fused pyrrolizidines was developed using N-aromatic zwitterions, aldehydes, and amino acids. The developed reactions proceed through azomethine ylides generated in situ from the decarboxylated reactions of aldehydes and amino acids followed by the [3 + 2] cycloaddition of N-aromatic zwitterions under mild reaction conditions.

Diversity Oriented Synthesis of Indoloazepinobenzimidazole and Benzimidazotriazolobenzodiazepine from N(1)-Alkyne-1,2-diamines.

A one-pot protocol for the diversity oriented synthesis of two N-polyheterocycles indoloazepinobenzimidazole and benzimidazotriazolobenzodiazepine from a common N(1)-alkyne-1,2-diamine building block is described. The approach involves sequential formation of benzimidazole through cyclocondensation and oxidation, which is followed by the formation of either an azepine ring (through alkyne activation and 6-endo-dig cyclization, 1,2-migration with ring expansion, and re-aromatization), or diazepine and triazole rings through 1,3-dipolar cycloaddition.

Metal-Free Decarboxylative Cyclization/Ring Expansion: Construction of Five-, Six-, and Seven-Membered Heterocycles from 2-Alkynyl Benzaldehydes and Cyclic Amino Acids.

A one pot synthesis of 1H-benzo[g]indoles, tetrahydrobenzo[h]quinolines, and naphtho[1,2-b]azepines from 2-alkynyl benzaldehydes and cyclic amino acids is reported. The salient feature of the strategy involves formation of three new bonds (one C-N and two C-C bonds) by a metal-free decarboxylation/cyclization/one-carbon ring expansion sequence in one pot.

One-pot synthesis of highly fluorescent pyrido[1,2-a]indole derivatives through C-H/N-H activation: photophysical investigations and application in cell imaging.

We describe a straightforward strategy for the synthesis of strongly fluorescent pyridoindoles by Pd-catalyzed oxidative annulations of internal alkynes with C-3 functionalized indoles through CH/NH bond activation in a one-pot tandem process. Mechanistic investigations reveal the preferential activation of NH indole followed by CH activation during the cyclization process. Photophysical properties of pyridoindoles exhibited the highest fluorescence quantum yield of nearly 80 %, with emission color varying from blue to green to orange depending on the substructures. Quantum mechanical calculations provide insights into the observed photophysical properties. The strong fluorescence of the pyrido[1,2-a]indole derivative has been employed in subcellular imaging, which demonstrates its localization in the cell nucleus.

Diversity-oriented synthesis of ketoindoloquinoxalines and indolotriazoloquinoxalines from 1-(2-nitroaryl)-2-alkynylindoles.

A one-pot protocol for the diversity-oriented synthesis of two indole-based annulated polyheterocycles, ketoindoloquinoxalines and indolotriazoloquinoxalines, has been described. The salient features of the methodology involves either a metal/O2-catalyzed aminooxygenation or a [3 + 2] cycloaddition pathway.

Gold-catalyzed sequential alkyne activation: one-pot synthesis of NH-carbazoles via cascade hydroarylation of alkyne/6-endo-dig carbocyclization reactions.

A simple and efficient one-pot protocol for the synthesis of NH-carbazoles has been described. The strategy comprises a one-pot reaction involving the treatment of 2-alkynyl indoles with arylacetylenes in the presence of an Au-Ag combination catalyst. The salient feature of the strategy involves sequential activation of terminal and internal alkynes leading to the cascade hydroarylation of terminal alkynes and 6-endo-dig carbocyclization reactions. The generality of the method has been demonstrated by using a series of 2-alkynyl indoles and arylacetylenes.

Synthesis of triazolo isoquinolines and isochromenes from 2-alkynylbenzaldehyde via domino reactions under transition-metal-free conditions.

We describe two simple straightforward syntheses of triazolo isoquinolines (3) and isochromenes (7) from 2-alkynylbenzaldehydes (1) as a common synthon. The synthetic strategy for 3 involves formation of the (E)-1-(2-nitrovinyl)-2-(alkynyl)benzene species 2 via condensation of synthon 1 with nitromethane followed by a [3 + 2] cycloaddition/extrusion of the nitro group/regioselective 6-endo cyclization domino sequence. In yet another strategy, the synthon 1 was condensed with nitromethane followed by electrophilic iodo cyclization of the resulting 2-nitro-1-(2-(alkynyl)phenyl)ethanol (6) to furnish iodo isochromene derivatives. The salient feature of the above two strategies involves formation of the corresponding heterocycles under metal-free conditions in good yields.

Contractions of 1,4-Diazepines to Pyrroles Triggered by Valence Tautomerization: A One-Pot Approach and Mechanism.

Herein, we describe the valence tautomerizations of fused 1,4-diazepines, which are reconstructed to give pyrrole derivatives and HCN gas. Several factors that influence the equilibrium between each valence tautomer of an 8π-electron diazepine skeleton are demonstrated. On the basis of these mechanistic studies, a cascade strategy for the construction of diazepines followed by ring contraction is developed to afford aryl- or alkyl-substituted pyrrolo[1,2-a]quinolines that are otherwise challenging to fabricate. In addition, further transformations of the obtained products highlight the advantages of the developed methodology.

A robust bis-rhodium(i) complex of π-extended planar, anti-aromatic hexaphyrin[1.0.1.0.1.0].

ß,ß'-Phenylene bridged hexaphyrin[1.0.1.0.1.0] (naphthorosarin), an expanded porphyrin possessing C3v-symmetry, has been shown to possess unique electronic features. We now report a bimetallic Rh(i)-complex of naphthorosarin retaining 24 π-antiaromatic characteristics. The two Rh(i) cations reside on opposite sides of the macrocyclic π-system and are separated at a distance consistent with a possible Rh(i)-Rh(i) metallic bond interaction.