Photoinduced Radical Annulations of Tetrahydroisoquinoline Derivatives with 2-Benzothiazolimines: Highly Diastereoselective Synthesis of Fused Hexahydroimidazo[2,1-a]isoquinolines

We report herein a photoinduced radical 1,3-dipolar cycloaddition between the 2-benzothiazolimines and tetrahydroisoquinoline derivatives with an organo-photocatalyst. A variety of benzothiazole-based hexahydroimidazo[2,1-a]isoquinoline architectures with great synthetic value were conveniently and efficiently constructed in moderate to good yields and excellent diastereoselectivities with highly tolerant functional groups. Moreover, the practicality and utility of this protocol were demonstrated by scale-up synthesis and facile elaboration. Preliminary mechanistic investigations indicated that the reaction proceeded via a visible-light-induced radical 1,3-dipolar cycloaddition pathway. This finding is expected to stimulate a more extensive exploration of the green and concise synthesis of structurally diverse heterocyclic molecules in the synthetic community.

Electrocatalytic dehydrogenative and defluorinative coupling between aldehyde-derived N,N-dialkylhydrazones and fluoromalonates: synthesis of 2-pyrazolines

An electrocatalytic synthesis of 2-pyrazolines via dehydrogenative and defluorinative cross-coupling reactions between (hetero)arylaldehyde-derived N,N-dialkylhydrazones and fluoromalonates is disclosed. Salient features of this work include (i) readily available starting materials, (ii) practical reaction conditions, and (ii) a formal oxidative (4 + 1)-cycloaddition via triple C-H bond functionalization. Cyclic voltammetry analyses support the electrocatalytic formation of an α-fluoromalonyl radical.

Photo-induced tungsten-catalyzed cascade synthesis of pyrrolo[2,1-a]isoquinoline-1,3-dicarboxylate and its reaction mechanism

A pyrrolo[2,1-a]isoquinoline core structure is prevalent in marine and other natural products. This article describes a tungsten-catalyzed [3+2] cycloaddition aromatization of dihydroisoquinoline ester and maleic anhydride or an acrylate. The photochemical reaction tolerates a range of functional groups such as ester, cyano, ketone, bromide, and alkene. It is shown that the cycloaddition-aromatization of 2-substitued acrylate catalyzed by a tungsten photocatalyst can be used to evaluate the leaving ability of the leaving group. Experiments done to determine the reaction mechanism revealed that the formation of an ion-pair intermediate generated in situ from dihydroisoquinoline ester and (Z)-4-methoxy-4-oxobut-2-enoic acid via the solvolysis of maleic anhydride with methanol is crucial for the cascade process to occur. The key cycloadduct acid intermediate derived from [3+2] cycloaddition was isolated and determined by X-ray crystallography.

Electrochemical Syntheses of Polycyclic Aromatic Hydrocarbons (PAHs)

Polycyclic aromatic hydrocarbons (PAHs) have surfaced as increasingly viable components in optoelectronics and material sciences. The development of highly efficient and atom-economic tools to prepare PAHs under exceedingly mild conditions constitutes a long-term goal. Traditional syntheses of PAHs have largely relied on multistep approaches or the conventional Scholl reaction. However, Scholl reactions are largely inefficient with electron-deficient substrates, require stoichiometric chemical oxidants, and typically occur in the presence of strong acid. In sharp contrast, electrochemistry has gained considerable momentum during the past decade as an alternative for the facile and straightforward PAHs assembly, generally via electro-oxidative dehydrogenative annulation, releasing molecular hydrogen as the sole stoichiometric byproduct by the hydrogen evolution reaction. This review provides an overview on the recent and significant advances in the field of electrochemical syntheses of various PAHs until January 2023.

Recent Advances in Biologically Active Coumarins from Marine Sources: Synthesis and Evaluation

Coumarin and its derivatives have significantly attracted the attention of medicinal chemists and chemical biologists due to their huge range of biological, and in particular, pharmacological properties. Interesting families of coumarins have been found from marine sources, which has accelerated the drug discovery process by inspiring innovation or even by the identification of analogues with remarkable biological properties. The purpose of this review is to showcase the most interesting marine-derived coumarins from a medicinal chemistry point of view, as well as the novel and useful synthetic routes described to date to achieve these chemical structures. The references that compose this overview were collected from PubMed, Mendeley and SciFinder.

Recent Advances in [3+2]-Cycloaddition-Enabled Cascade Reactions: Application to Synthesize Complex Organic Frameworks

Many natural products and biologically important complex organic scaffolds have convoluted structures around their core skeleton. Interestingly, with just changing the outskirts, the core reflects new and unique degrees of various physical and chemical properties. A very common but intriguing core is a five-membered ring horning heaps of organic molecules crafts. The power of [3+2] cycloaddition reactions to generate five-membered ring systems allocate chemists to envision synthetic procedures of wonder molecules and if it is facilitating a cascade sequence, then the end product will imbibe significant level of complexity having applications in medicinal and pharmaceutical fields. This Account highlights the broad interest in assembling recent advances in cascade reactions involving [3+2] cycloaddition as the power tool in order to conceive breakthrough organic architectures reported in the last ten years. We foresee that our comprehensive collection of astonishing [3+2] cycloaddition enabled cascades will provide valuable insights to polycyclic molecular construction and perseverant approach towards nonconventional synthetic procedures to the organic community.

1 Introduction

2 Synthesis of Oxindoles Skeleton

3 Synthesis of Oxazoles Skeleton

4 Synthesis of Oxadiazoles Skeleton

5 Synthesis of Nitrogen-Containing Heterocycles

6 Synthesis via Formal [3+2] Cycloaddition

7 Synthesis of Miscellaneous Scaffolds

8 Conclusion

Recent progress in the synthesis of pyrrolo[2,1-a]isoquinolines

Pyrrolo[2,1-a]isoquinolines occur frequently in a large number of bioactive natural products and pharmaceutically important molecules. The synthesis of pyrrolo[2,1-a]isoquinoline derivatives is an easy and useful way to produce artificial molecules with potential applications. A huge number of excellent methodologies for constructing pyrrolo[2,1-a]isoquinolines have been reported in the last decade. This review summarizes the recent advances in this research field covering from 2011 to 2021.

Tungsten catalysed decarboxylative [3 + 2] cycloaddition aromatization: one-pot synthesis of trifluoromethyl-pyrrolo[2,1-a]isoquinolines with visible light irradiation

Trifluoromethyl-pyrrolo[2,1-a]isoquinolines, which are difficult to prepare via traditional methods, could be readily prepared via a tungsten-catalysed decarboxylative [3 + 2] cycloaddition aromatization process.

Stereoselective synthesis of fused-, spiro- and bridged heterocycles via cyclization of isoquinolinium salts: A recent update

Isoquinoline and its derivatives are ubiquitous in natural alkaloids, synthetic materials and pharmaceuticals with broad spectrum of biological activities. In particular, isoquinolinium salts are important in organic synthesis because they...

Recent advances in the electrochemical reactions of nitrogen-containing organic compounds

The electrochemical reaction of amines, nitriles, amides, nitroaromatics, and imines has been proven to be a valuable method for the synthesis of various nitrogen-containing organic compounds.

Electrochemical Generation of a Nonstabilized Azomethine Ylide: Access to Substituted N-Heterocycles

Azomethine ylides are fascinating 1,3-dipoles for [3 + 2] cycloaddition reactions toward the construction of N-heterocycles. Herein, an efficient and environmentally benign electrochemical approach for the generation of a nonstabilized azomethine ylide has been established under metal-free and external oxidant-free conditions. The resulting 1,3-dipole undergoes a [3 + 2] cycloaddition reaction with olefins. This electrosynthetic methodology indulges a straightforward and facile approach for the construction of substituted pyrrolidines.

Electrochemically promoted oxidative α-cyanation of tertiary and secondary amines using cheap AIBN

The electrochemical α-cyanation of tertiary and secondary amines has been developed by using a cheap cyanide reagent, azobisisobutyronitrile (AIBN). The CN radical, generated through n-Bu₄NBr-meidated electrochemical oxidation, participates in a novel α-cyanation reaction under exogenous oxidant-free conditions.

CuBr/NHPI co-catalyzed aerobic oxidative [3 + 2] cycloaddition-aromatization to access 5,6-dihydro-pyrrolo[2,1-a]isoquinolines

An efficient and enviromentally friendly CuBr/NHPI co-catalyzed aerobic oxidative [3 + 2] cycloaddition-aromatization cascade was realized with N-substituted tetrahydroisoquinolines and electron-deficient olefins. Under the mild conditions, the reaction proceeded smoothly and displayed excellent functional group tolerance, affording 5,6-dihydro-pyrrolo[2,1-a]isoquinolines in good to high yields. This protocol exhibits a broad substrate scope to both N-alkyl tetrahydroisoquinolines and dipolarophile substrates.

Electrochemical one-pot synthesis of five-membered azaheterocycles via [4 + 1] cyclization

Five-membered N-heterocycles, such as oxadiazoles, thiadiazoles, oxazolines and imidazoles, have been prepared via electrochemical oxidation/[4 + 1] cyclization/dehydrogenative aromatization in one pot from readily available materials.

Synthesis of indolizines from pyridinium 1,4-zwitterionic thiolates and propiolic acid derivatives via a formal [4 + 1] pathway

Indolizines were synthesized from 1,4-zwitterionic thiolates and propiolic acid derivatives mediated by triethylamine via a formal [4 + 1] pathway.