Synthesis of pentacyclic 13-azadibenzo[a,de]anthracenes via anionic cascade ring closure

One-Step Synthesis of 7-Bromobenzo[c]chromeno[4,3,2-gh]phenanthridines through a Sequential Bromination/Cyclization/Aromatization Reaction Using N-Bromosuccinimide (NBS)

Herein, metal- and oxidant-free synthesis of 7-bromobenzo[c]chromeno[4,3,2-gh]phenanthridines is reported using N-bromosuccinimide. Sequential regioselective bromination, intramolecular ring cyclization, and aromatization reactions occur in a single step through a successive radical-catalyzed pathway. The mechanistic pathway for the cyclization is supported by a DFT study. Selective bromination in the fully aromatic skeleton is accomplished without involving additional aromatic electrophilic ring bromination. As a synthetic application, the Suzuki coupling reaction of compound 5a with boronic acid is reported to get compound 8a. Aggregation-induced emission of one of the synthesized compounds (5h) is also investigated in THF/hexane solvent along with concentration-dependent emission spectroscopy.

Access to ortho-Hydroxyphenyl Ketimines via Imine Anion-Mediated Smiles Rearrangement

We have achieved a facile access to N-(2-halophenyl)-2-hydroxyphenylimine derivatives via imine anion-mediated Smiles rearrangement. When 2-(2-halophenoxy)benzonitriles were treated with 1.2-1.4 equiv of organolithium reagents, nucleophilic addition to the nitrile group followed by Smiles rearrangement occurred to give various N-(2-halophenyl)-2-hydroxyphenylimine derivatives, which are sometimes difficult to synthesize by the conventional acid-promoted condensation reaction between carbonyl compounds and aniline derivatives, in good to excellent chemical yields (up to 91%).

DMSO-assisted environmentally benign synthesis of benzo[c]-chromeno[4,3,2-gh]phenanthridines by remote oxidative hetero cross-coupling cyclization and aromatization reaction

An unprecedented metal-free and catalyst-free synthesis of benzo[c]chromeno[4,3,2-gh]phenanthridine derivatives, a class of 1,6-diheterophenalenoid heterocycle, is reported for the first time. The oxidative cross-coupling reaction for the remote cyclization is achieved through the in situ generated o-quinone methide intermediate followed by an electrocyclic ring closure reaction. The aromatization of the cyclohexane ring is achieved by sequential H shift, hydroxylation, and elimination reaction. DMSO-assisted concomitant cyclization and aromatization reactions are also disclosed for the first time.

Functionalization of 4-bromobenzo[c][2,7]naphthyridine via regioselective direct ring metalation. A novel approach to analogues of pyridoacridine alkaloids

Readily available 4-bromobenzo[c][2,7]naphthyridine undergoes regioselective direct ring metalation at C-5 with TMPMgCl∙LiCl at −40 °C. Quenching with various electrophiles gives a broad range of 5-substituted products, which are building blocks for the synthesis of heterocyclic natural products and analogues thereof. In combination with a Parham-type cyclization a novel approach to pyrido[4,3,2-mn]acridones has been worked out.

Cascade intramolecular imidoylation and C–H activation/annulation of benzimidoyl chlorides with alkynes: one-pot synthesis of 7H-dibenzo[de,h]quinoline analogues

Described herein is a cascade Lewis acid-promoted intramolecular Friedel–Crafts-type imidoylation and Rh(iii)-catalyzed C–H activation/annulation of benzimidoyl chlorides and alkynes, providing a divergent synthetic shortcut to 7H-dibenzo[de,h]quinoline analogues.

Heterocyclic Nanographenes and Other Polycyclic Heteroaromatic Compounds: Synthetic Routes, Properties, and Applications

Two-dimensionally extended, polycyclic heteroaromatic molecules (heterocyclic nanographenes) are a highly versatile class of organic materials, applicable as functional chromophores and organic semiconductors. In this Review, we discuss the rich chemistry of large heteroaromatics, focusing on their synthesis, electronic properties, and applications in materials science. This Review summarizes the historical development and current state of the art in this rapidly expanding field of research, which has become one of the key exploration areas of modern heterocyclic chemistry.

Hydride-induced anionic cyclization: an efficient method for the synthesis of 6-H-phenanthridines via a transition-metal-free process

A novel procedure for hydride-induced anionic cyclization has been developed. It includes the reduction of a biaryl bromo-nitrile with a nucleophilic aromatic substitution (S(N)Ar). A range of polysubstituted 6-H-phenanthridines were so obtained in moderate to good yield with good substrate tolerance. This method involves a concise transition-metal-free process and was applied to synthesize natural alkaloids.

Synthesis and structure-affinity relationships of selective high-affinity 5-HT(4) receptor antagonists: application to the design of new potential single photon emission computed tomography tracers

The work described herein aims at finding new potential ligands for the brain imaging of 5-HT(4) receptors (5-HT(4)Rs) using single-photon emission computed tomography (SPECT). Starting from the nonsubstituted phenanthridine compound 4a, exhibiting a K(i) value of 51 nM on the 5-HT(4)R, we explored the structure-affinity in this series. We found that substitution in position 4 of the tricycle with a fluorine atom gave the best result. Introduction of an additional nitrogen atom inside the tricyclic framework led to an increase of both the affinity and selectivity for 5-HT(4)R, suggesting the design of the antagonist 4v, exhibiting a high affinity of 0.04 nM. Several iodinated analogues were then synthesized as potential SPECT tracers. The iodinated compound 11d was able to displace the reference radioiodinated 5-HT(4)R antagonist (1-butylpiperidin-4-yl)methyl-8-amino-7-iodo[(123)I]-2,3-dihydrobenzo[b][1,4]dioxine-5-carboxylate {[(123)I]1, [(123)I]SB 207710} both in vitro and in vivo in brain. Compound 11d was radiolabeled with [(125)I]iodine, providing a potential SPECT candidate for brain imaging of 5-HT(4)R.

Total synthesis of ascididemin via anionic cascade ring closure

A new and convergent synthesis of ascididemin is presented. Using an anionic cascade ring closure as the key step, this natural product is obtained in 45% overall yield in just 6 steps starting from 2'-fluoroacetophenone. This new approach was extended to the synthesis of a new isomer of ascididemin.

Highly Efficient Synthesis of Stereodefined Multisubstituted 1,4-Dicyano- and 1-Cyano-1,3-butadienes and Their Reactions with Organolithium Reagents

Stereodefined multisubstituted 1-cyano- and 1,4-dicyano-1,3-butadiene derivatives were obtained in excellent yields of the isolated product from their corresponding monohalo- and dihalobutadienes and CuCN. This reaction proceeded with high stereoselectivity and retention of the stereochemistry of the starting halobutadienes. A study of the utility of the thus-obtained 1-cyano- and 1,4-dicyano-1,3-butadiene derivatives was demonstrated by their reactions with organolithium reagents. 2H-Pyrrole or iminocyclopentadiene derivatives were formed in high yields from 1-cyano-4-halo-1,3-butadienes and organolithium reagents. When 1,4-dicyano-1,3-butadienes were treated with organolithium reagents followed by trapping with electrophiles, a tandem process took place to afford 2H-pyrrolyl nitriles in excellent yields. Reduction of 1,4-dicyano-1,3-butadiene derivatives with LiAlH4 showed novel reaction patterns relative to normal nitriles.

Synthesis of 4-phenoxybenzamide adenine dinucleotide as NAD analogue with inhibitory activity against enoyl-ACP reductase (InhA) of Mycobacterium tuberculosis

The chemical synthesis of 4-phenoxybenzamide adenine dinucleotide (3), a NAD analogue which mimics isoniazid-NAD adduct and inhibits Mycobacterium tuberculosis NAD-dependent enoyl-ACP reductase (InhA), is reported. The 4-phenoxy benzamide riboside (1) has been prepared as a key intermediate, converted into its 5'-mononucleotide (2), and coupled with AMP imidazolide to give the desired NAD analogue 3. It inhibits InhA with IC50 = 27 microM.