Copper-Carbene-Triggered Electrophilic Cyclization of o-Hydroxyarylenaminones with 3-Diazoindolin-2-imines: Synthesis of 3-Indolyl-4H-chromen-4-ones and Pyrido[2,3-b:6,5-b′]diindoles

Visible-Light-Induced Synthesis of 3-Alkyl Chromones under Catalyst- and Additive-Free Conditions

Herein, we reported an efficient and facile visible-light-induced 3-alkyl chromone synthesis from easily accessible o-hydroxyaryl enaminones and α-diazo esters. In this protocol, excellent yields were obtained with a broad substrate scope at room temperature, tolerating various functional groups. Of note is that this eco-friendly methodology features catalyst- and additive-free, mild reaction conditions, simple operation procedure, and easy scale-up, which affords a convenient pathway for the preparation of 3-alkyl chromones. Experimental results and density functional theory (DFT) computation analyses confirm the participation of carbene species and active cyclopropane intermediate.

Rhodium Catalyzed [4 + 1]-Annulation of o-Acylanilines with 3-Diazoindoline-2-imines

An efficient rhodium catalyzed [4 + 1]-annulation of o-acylanilines with 3-diazoindoline-2-imines has been successfully accomplished for the synthesis of spiroindolines in good to excellent yield. The reaction occurs through formation of N-ylide followed by cyclization and showed good tolerance to various functional groups. Gram-scale synthesis, diastereoselective construction of tetrasubstituted indoline, synthesis of spirooxindole, and isolation of potential intermediates have also been demonstrated.

Versatile access to nitrogen-rich π-extended indolocarbazoles via a Pictet–Spengler approach

A bidirectional Pictet-Spengler Reaction allows easy access to nitrogen-rich aromatics with seven fused rings. Photophysical measurements and computational methods show significant differences to parent N-heteropolycycles with fewer nitrogen atoms.

Olefination of 3-Diazoindolin-2-imines with Hydrazones: An Approach toward Stereoselective Synthesis of (E)-3-Arylideneindolin-2-imines

Stereoselective synthesis of (E)-3-arylideneindolin-2-imines from 3-diazoindolin-2-imines and hydrazones was achieved using copper bromide as the catalyst. The olefination reaction proceeded via copper-catalyzed aerobic oxidation of hydrazones to diazo compounds and copper-catalyzed cross coupling of two different diazo components in a tandem manner.

Efficient Synthesis of Dipyrrolobenzenes and Dipyrrolopyrazines via Bidirectional Gold Catalysis: a Combined Synthetic and Photophysical Study

New N-heterocyclic fluorophores are sought-after compounds for organic electronic devices. Here, we report on a straightforward synthesis to access meta/para-dipyrrolobenzenes and para-dipyrrolopyrazines in high yields using a bidirectional gold-catalyzed cyclization strategy. The versatility of our reaction protocol was showcased by preparing dipyrroloarenes with different substituents, various functional groups, and in a multitude of substitution patterns. Furthermore, we showed that the dipyrroloarenes can be post-modified by N-alkylation to improve the solubility or bromination to yield precursors for further derivatization via cross-coupling. Investigation of the photophysical properties of the─mostly unprecedented─dipyrroloarenes identified strong blue emitters such as the diphenyl meta-dipyrrolobenzene with a quantum yield of 98%. Moreover, we showed that changes in the solvent polarity or interactions with Lewis acids such as borane can be used to fine-tune the photophysical properties of the fluorophores.

Recent advances in the synthesis of indole embedded heterocycles with 3-diazoindolin-2-imines

The preparations, reactivity and synthetic applications of 3-diazoindolin-2-imines, a valuable class of α-diazo amidines, are reviewed.

Recent Advances in Organic Synthesis Based on N,N-Dimethyl Enaminones

Enaminones are gaining increasing interest because of their unique properties and their importance in organic synthesis as versatile building blocks. N,N-Dimethyl enaminones offer a better leaving group (a dimethylamine group) than other enaminones, and allow further elaboration via a range of facile chemical transformations. Over the past five years, there have been an increasing number of reports describing the synthetic applications of N,N-dimethyl enaminones. This review provides a comprehensive overview on the synthetic applications of N,N-dimethyl enaminones that have been reported since 2016.

1 Introduction

2 Direct C(sp2)–H α-Functionalization

2.1 Synthesis of α-Sulfenylated N,N-Dimethyl Enaminones

2.2 Synthesis of α-Thiocyanated N,N-Dimethyl Enaminones

2.3 Synthesis of α-Acyloxylated N,N-Dimethyl Enaminones

3 Functionalization Reactions via C=C Double Bond Cleavage

3.1 Synthesis of Functionalized Methyl Ketones

3.2 Synthesis of α-Ketoamides, α-Ketoesters and 1,2-Diketones

3.3 Synthesis of N-Sulfonyl Amidines

4 Construction of All-Carbon Aromatic Scaffolds

4.1 Synthesis of Benzaldehydes

4.2 Synthesis of the Naphthalenes

5 Construction of Heterocyclic Scaffolds

5.1 Synthesis of Five-Membered Heterocycles

5.2 Synthesis of Six-Membered Heterocycles

5.3 Synthesis of Quinolines

5.4 Synthesis of Functionalized Chromones

5.5 Synthesis of Other Fused Polycyclic Heterocycles

6 Conclusions and Perspectives

Selectfluor-triggered fluorination/cyclization of o-hydroxyarylenaminones: A facile access to 3-fluoro-chromones

A fast and efficient Selectfluor-triggered fluorination/cyclization reaction of o-hydroxyarylenaminones has been successfully developed. The reaction successfully provides an expedient method for the synthesis of 3-fluoro-chromones promoted by potassium carbonate, which shows readily available starting materials and is easy to operate. In addition, a plausible mechanism of this tandem cyclization reaction was proposed where 4 H-chromen-4-one, 2-(dimethylamino)-3,3-difluorochroman-4-one, and 3,3-difluoro-2-hydroxychroman-4-one were not found to be the reactive intermediates. Moreover, these novel compounds have been obtained in moderate to good yields, and their structures have been confirmed by 1H NMR, 13C NMR, and high-resolution mass spectrometry.

Synthesis of 3-halochromones with simple KX halogen sources enabled by in situ halide oxidation

An in situ oxidation strategy for generating molecular halogen has been developed for the synthesis of 3-halochromones by employing simple potassium halides as halogen sources.

Toward C2-nitrogenated chromones by copper-catalyzed β-C(sp2)–H N-heteroarylation of enaminones

The synthesis of C2-nitrogenated chromones has been performed via reactions of enaminones and nitrogen nucleophiles based on an unconventional β-C–H bond functionalization and a featured chromone annulation of enaminones.

Transition metal-free synthesis of 3-trifluoromethyl chromones via tandem C–H trifluoromethylation and chromone annulation of enaminones

The synthesis of 3-trifluoromethyl chromones has been realized via transition metal-free reactions of o-hydroxyphenyl enaminones and the Langlois reagent via cascade C–H trifluoromethylation and chromone annulation.