Domino or Single-Step Tsuji-Trost/Heck Reactions and Their Application in the Synthesis of 3-Benzazepines and Azepino[4,5-b]indole Ring Systems

Recent Advances in Palladium-Catalyzed Asymmetric Heck/Tsuji-Trost Reactions of 1,n-Dienes

Transition-metal catalyzed tandem asymmetric reactions were powerful tools to access various chiral compounds. Many strategies have been developed for the coupling of 1,n-dienes with aryl halides via a tandem Heck/Tsuji-Trost process. However, the control of regio- and stereo-chemistry remains a challenging task. This minireview details the recent advances in the field of asymmetric Heck/Tsuji-Trost reactions catalyzed by palladium complex, which have opened new opportunities and expanded our understanding in this area of research in recent years.

Synthesis of Azepino[4,5-b]indole via Ring Expansion of Tetrahydro-β-carbolines Ammonium Ylide

The formal cyclization strategy was generally used to construct azepino[4,5-b]indole. Herein, we reported a novel and expeditious protocol for the synthesis of quaternary carbon azepino[4,5-b]indole via ring expansion of ammonium ylide, which was formed by the reaction of tetrahydro-β-carbolines with the diazo compound. The easily available substrates, mild reaction conditions, and broad functional tolerance rendered this method a practical strategy that may significantly afford an efficient method of scaffold hopping in drug discovery.

Regioselective Synthesis of Indole-Fused Seven-Membered N-Heterocycles via Photoredox-Catalyzed Intramolecular Cyclization

Herein, we describe the construction of indole-fused seven-membered N- and O-heterocycles from indolyl α-diazocarbonyls via photoredox-catalyzed intramolecular cyclization. The photoredox process features operational simplicity, mild conditions, and as low as 0.1 mol % catalyst loading. The tricyclic heterocycles are obtained in yields of 24 to 67% with excellent regioselectivity. The practicality of this protocol is further demonstrated by gram-scale reactions carried out in both batch and continuous flow.

Pd-Catalyzed Domino Reactions Involving Alkenes To Access Substituted Indole Derivatives

Palladium-catalyzed domino reactions are advanced tools in achieving various nitrogen-containing heterocycles in an efficient and economical manner due to the reduced number of steps in the process. This review highlights recent advances in domino processes aimed at the synthesis of indole derivatives and polycyclic systems containing the indole nucleus in intra/intra- or intra/intermolecular reactions. In particular, we consider domino processes that involve a double bond in a step of the sequence, which allow the issue of regioselectivity in the cyclization to be faced and overcome. The different sections in this review focus on the synthesis of the indole nucleus and functionalization of the scaffold starting from different substrates that have been identified as activated starting materials, which involve a halogenated moiety or unactivated unsaturated systems. In the former case, the reaction is under Pd(0) catalysis, and in the second case a Pd(II) catalytic species is required and then an oxidant is necessary to reconvert the Pd(0) into the active Pd(II) species. On the other hand, the second method has the advantage that it uses easy available and inexpensive substrates.

1 Introduction

2 Indole Scaffold Synthesis

2.1 Activated Substrates

2.2 Unactivated Substrates

3 Functionalization of Indole Scaffold

3.1 Activated Substrates

3.2 Unactivated Substrates

4 Conclusions

Chalcone-Based Pyridinium Salts and Their Diastereoselective Dearomatization To Access Bibridged Benzoazepines

New chalcone-based pyridinium salts have been successfully exploited, which could smoothly participate in the highly diastereoselective dearomatization with binucleophilic enaminones by taking advantage of their multiple reactive sites to construct bibridged benzoazepines in up to 89% yields. The key to the success was the skillful and unprecedented C-3 functionalization of the new pyridinium salts. This work not only provides a kind of novel pyridinium salt synthon but also achieves the first C-3 functionalization of pyridinium salts to construct complex and challenging bibridged benzoazepines with high synthetic efficiency.

Friedel–Crafts Chemistry. Part 53. Divergent and Diversity-Oriented Synthesis of Condensed Indole Scaffolds via Friedel–Crafts Ring Closure Approach

A series of indole-fused medium-sized N-heterocyclic systems 10a–h were prepared from laboratory-synthesized indole-based esters 9a–h via intramolecular Friedel–Crafts cyclizations induced by both trifluoromethanesulfonic acid and AlCl3/CH3NO2 catalysts under suitable conditions. The synthetic sequence to precursors 9a–h that started from simple N-methylindole-2-carboxylic acid involved conversion to aminoindoles 2a, b, reaction with α,β-unsaturated acid chlorides to yield acyclic amides 5a–d, ring closure to tricyclic lactams 6a–d, and carbonyl reduction to respective pyrido and azepino tricyclic amines 7a–d, which finally underwent N-alkylations with α- or β-haloesters to produce the required ester precursors. The structures of synthesized compounds without stereochemical implications are established using both spectral and analytical data.

A simple and efficient method for constructing azepino[4,5-b]indole derivatives via acid catalysis

A new and efficient synthetic methodology has been developed to prepare azepino[4,5-b]indole derivatives under Brønsted acid catalysis.

Distinguishing rotamers in N-trifluoroacetyl-3-benzazepine derivatives

This paper provides the full (13) C NMR assignments for the trifluoroacetamides of five potentially appetite-reducing 5-HT2C benzazepine receptor agonists and two open-ring synthetic precursors. These compounds exist in solution as mixtures of two rotamers for each of which the (13) C NMR signals have now been assigned with the assistance of 2D NMR experiments and the carbonyl-induced shifts of the neighboring (13) CH2 resonances and long-range (13) C/(19) F couplings.

Regioselective alkylation of 1,3,4,5-tetrahydrobenzo[d]azepin-2-one and biological evaluation of the resulting alkylated products as potentially selective 5-HT₂c agonists

The benzazepine ring system has offered interesting CNS-active medicinal agents. Taking this privileged structure as the basic scaffold, [Formula: see text] and/or [Formula: see text]-alkylated benzazepin-2-one derivatives and their reduced analogs have been prepared as potential [Formula: see text] receptor agonists. The selective alkylation at the [Formula: see text] and/or [Formula: see text] positions of this seven-membered lactam ring is here reported for the first time under different reaction conditions. The synthesized compounds were evaluated for their biological profile as potential [Formula: see text] agonists using a classic pharmacological approach. Three derivatives (15, 17, and 20) have shown promising [Formula: see text] agonistic activity which can be further optimized as anti-obesity agents for the treatment of male sexual dysfunction. Further, a homology model for [Formula: see text] receptor was generated using MODELLER, and ligand-receptor interactions for these potential molecules were studied.