Intramolecular Cycloaddition of Azomethine Ylides in the Preparation of Pyrrolidino[2‘,3‘:3,4]pyrrolidino[1,2- a]benzimidazoles

Expeditious synthesis of highly substituted 3(2H)-furanone and quinoline by microwave assisted reaction between aldonitrones and dibenzoylacetylene

Microwave assisted reaction between various aldonitrones and dibenzoylacetylene gave 2-hydroxy-2,5-diphenyl-4-(phenylamino)furan-3(2H)-one (5) and (3-hydroxy-2-phenylquinolin-4-yl)(phenyl)methanone (8) arising through two distinct reaction pathways in good yields. Compared to reactions carried out under thermal...

Design, synthesis and antiproliferative activity of decarbonyl luotonin analogues

A small library of benzimidazole-fused pyrrolo[3,4-b]quinoline has been synthesized from readily available benzimidazole 2-carbaldehyde and various substituted arylamines in good to excellent yields utilizing an intramolecular Povarov reaction catalyzed by boron trifluoride diethyl etharate as the key final step. The compounds thus synthesized can be considered as decarbonyl analogues of the anticancer alkaloid luotonin A and were evaluated in a DNA relaxation assay for their ability to inhibit human topoisomerase I. Interestingly, two of the compounds showed a remarkable activity that is comparable to that of the standard drug camptothecin. The compounds were also evaluated for their cytotoxic effect in four highly aggressive human cancer cell lines, namely KB, MDA-MB231 (breast), LNCap (prostate), and HT1080 (fibrosarcoma). Some of the compounds obtained showed promising cytotoxicities for these four cell lines.

Synthesis, Spectroscopic, X-ray Diffraction and DFT Studies of Novel Benzimidazole Fused-1,4-Oxazepines

A series of benzimidazole-tethered oxazepine heterocyclic hybrids has been synthesized in good to excellent yields from an N-alkylated benzimidazole 2-carboxaldehyde, which in turn was accomplished from o-phenylenediamine in three good yielding steps. The calculated molecular structure of compounds 2-methyl-4-(2-((phenylimino)methyl)-1H-benzo-[d]imidazol-1-yl)-butan-2-ol 9 and 10 3,3-dimethyl-N-phenyl-1,2,3,5-tetrahydrobenzo-[4,5]imidazo[2,1-c][1,4]oxazepin-5-amine using the B3LYP/6-31 G(d, p) method were found to agree well with their X-ray structures. The charge distributions at the different atomic sites were computed using the natural bond orbital (NBO) method. The regions of electrophilic and nucleophilic reactivity were shown using a molecular electrostatic potential (MEP) map. In addition, the frontier molecular orbitals of these compounds were discussed at the same level of theory. Nonlinear optical (NLO) properties have also been investigated by computational hyperpolarizability studies, and it was found that Compound 9 is the best candidate for NLO applications.

Synthesis of novel imidazole-based triheterocycles via a domino Ugi/Michael reaction and silver-catalyzed heteroannulation

An efficient and diversity-oriented synthetic strategy for novel triheterocyclic imidazo-pyrrolo-pyrazine/diazepine/diazocine derivatives is elaborated.

Diastereoselective synthesis of novel tetra-and pentacyclic annulated coumarino-δ-sultam pyrrolidine, pyrrolizidine, pyrrolothiazole and isoxazolidine derivatives via intramolecular 1,3-dipolar cycloadditions

A facile and efficient strategy towards the novel tetra- and pentacyclic annulated coumarino-δ-sultam pyrrolidine, pyrrolizidine, pyrrolothiazole and isoxazolidine via intramolecular 1,3-dipolar cycloadditions of is described.

Diversity oriented synthesis of benzimidazole-based biheterocyclic molecules by combinatorial approach: a critical review

Because of the wide ranging bioactivities associated with the benzimidazole nucleus, this review highlights the advances made in the synthesis of benzimidazole-based biheterocyclic molecules by combinatorial approaches.

Ethyl 1-benzyl-1,2,3,3a,4,10b-hexa-hydro-pyrrolo-[2',3':3,4]pyrrolo-[1,2-a]benzimidazole-2-carboxyl-ate

The title mol­ecule, C₂₂H₂₃N₃O₂, was obtained via an intra­molecular cyclo­addition of an azomethine ylide and an alkene tethered by a benzimidazole unit. The benzoimidazole unit is essentially planar, with an r.m.s. deviation of 0.0087 Å from the nine constituent atoms. It has a cis fusion of the two pyrrolidine rings as well as a cis ester appendage. The two pyrrolidine rings rings have envelope conformations. The crystal packing is stabilized by aromatic π–π stacking of parallel benzimidazole ring systems, with a centroid-to-centroid distance of 3.518 (6) Å. Weak inter­molecular C—H⋯O contacts may also play a role in the stability of the packing.

Stereoselective formation of fused tricyclic amines from acyclic aldehydes by a cascade process involving condensation, cyclization, and dipolar cycloaddition

The preparation of tricyclic amines from acyclic precursors is described using a cascade of tandem reactions involving condensation of an aldehyde with a primary amine, cyclization (with displacement of a halide), and then in situ deprotonation or decarboxylation to give an azomethine ylide or nitrone followed by intramolecular dipolar cycloaddition. The methodology is straightforward, and the aldehyde precursors are prepared easily and quickly in high yield using nitrile alkylations followed by DIBAL-H reduction. The relative ease of reaction of various substrates with different tether lengths between the aldehyde and the halide or dipolarophile has been studied. Several primary amines including simple amino acids such as glycine, alanine, and phenylalanine and derivatives such as glycine ethyl ester and also hydroxylamine have been investigated. High yields are obtained in the formation of different tricyclic ring sizes; the dipolar cycloaddition necessarily creates a five-membered ring, and we have investigated the formation of five- and six-membered rings for the other two new ring sizes. In all cases, yields are high (except when using glycine when the tether to the terminal alkene dipolarophile leads to a six-membered ring), and most efficient is the formation of the tricyclic product in which all five-membered rings are formed. Examples with an alkyne as the dipolarophile were also successful. In all the reactions studied, the products are formed with complete regioselectivity and remarkably with complete stereoselectivity. The key step involves the formation of three new rings and potentially up to four new stereocenters in a single transformation. The power of the chemistry was demonstrated by the synthesis of the core ring systems of the alkaloids (+/-)-scandine and (+/-)-myrioneurinol and the total syntheses of the alkaloids (+/-)-aspidospermine, (+/-)-quebrachamine, and (+/-)-aspidospermidine.

Controlling Selectivity for Cycloadditions of Nitrones and Alkenes Tethered by Benzimidazoles: Combining Experiment and Theory

Herein we describe a combined experimental/theoretical study on the effects of substituents on regio- and stereoselectivity in intramolecular 1,3-dipolar cycloadditions of nitrones and alkenes tethered by benzimidazoles. By employing a large substituent at position R² or R³, complete selectivity was achieved for either the fused or bridged cycloadduct, respectively. In addition, these cycloadducts were formed as single diastereomers in all of the cycloadditions examined.

Microwave-Assisted Tandem Processes for the Synthesis of N-Heterocycles

Over the years, microwave-assisted organic synthesis (MAOS) became a commonly applied mainstream tool for the synthesis of heterocyclic compounds. The broad range of emerging applications in this field is mainly due to the significant contribution of MAOS to the development of ecofriendly processes. Various transformations have been developed for the synthesis of N-heterocycles under microwave conditions, including fast and selective processes. Tandem reactions involving greener reaction media, solvent-free conditions, and solid-phase synthesis are of exceptional interest in this area. In most transformations, microwave conditions dramatically enhanced reaction rates, as well as provided improved yields. This account highlights the most recent advancements in MAOS-based tandem processes for the synthesis of N-heterocycles.