LDA-Promoted Synthesis of 3-Amino Furans by Selective Lithiation of Enaminones

Biomass to Aromatic Amine Module: Alkali Catalytic Conversion of N-Acetylglucosamine into Unsubstituted 3-Acetamidofuran by Retro-Aldol Condensation

Aminofurans are widely used in drug synthesis as aromatic modules analogous to aniline. However, unsubstituted aminofuran compounds are difficult to prepare. In this study, a process for the selective conversion of N-acetyl-d-glucosamine (NAG) into unsubstituted 3-acetamidofuran (3AF) is developed. The yield of 3AF from NAG catalyzed by a ternary Ba(OH)₂ -H₃ BO₃ -NaCl catalytic system in N-methylpyrrolidone at 180 °C for 20 min can reach 73.9 %. Mechanistic studies reveal that the pathway to 3AF starts with a base-promoted retro-aldol condensation of the ring-opened NAG, affording the key intermediate N-acetylerythrosamine. Judicious selection of the catalyst system and conditions enables the selective conversion of biomass-derived NAG into 3AF or 3-acetamido-5-acetylfuran.

Thiazole-5-carbaldehyde Synthesis by Cascade Annulation of Enaminones and KSCN with Dess-Martin Periodinane Reagent

The Dess-Martin periodinane (DMP) reagent-mediated reactions of tertiary enaminones with potassium thiocyanate for the synthesis of thiazole-5-carbaldehydes are developed. The product formation involves cascade hydroxyl thiocyanation of the C═C double bond, intramolecular hydroamination of the C≡N bond, and thiazole annulation by condensation on the ketone carbonyl site, representing novel reaction pathways in the reactions between enaminones and thiocyanate salt. DMP plays dual roles in mediating the free radical thiocyanation and inducing the unconventional selective thiazole-5-carbaldehyde formation by masking the in situ generated formyl group during the reaction process.

One-pot synthesis of 3-aminofurans using a simple and efficient recyclable CuI/[bmim]PF6 system

A one-pot three-component reaction of several 2-ketoaldehydes, secondary amines and terminal alkynes to access 3-aminofurans proceeded well in [bmim][PF₆] using a simple and cheap CuI catalyst. The resultant 3-aminofuran products were easily isolated using diethyl ether and the CuI/[bmim][PF₆] system was reused six times with a slight decrease in the activity.

Alkynoates as Versatile and Powerful Chemical Tools for the Rapid Assembly of Diverse Heterocycles under Transition-Metal Catalysis: Recent Developments and Challenges

Heterocycles, heteroaromatics and spirocyclic entities are ubiquitous components of a wide plethora of synthetic drugs, biologically active natural products, marketed pharmaceuticals and agrochemical targets. Recognizing their high proportion in drugs and rich pharmacological potential, these invaluable structural motifs have garnered significant interest, thus enabling the development of efficient catalytic methodologies providing access to architecturally complex and diverse molecules with high atom-economy and low cost. These chemical processes not only allow the formation of diverse heterocycles but also utilize a range of flexible and easily accessible building units in a single operation to discover diversity-oriented synthetic approaches. Alkynoates are significantly important, diverse and powerful building blocks in organic chemistry due to their unique and inherent properties such as the electronic bias on carbon-carbon triple bonds posed by electron-withdrawing groups or the metallic coordination site provided by carbonyl groups. The present review highlights the comprehensive picture of the utility of alkynoates (2007-2019) for the synthesis of various heterocycles (> 50 types) using transition-metal catalysts (Ru, Rh, Pd, Ir, Ag, Au, Pt, Cu, Mn, Fe) in various forms. The valuable function of versatile alkynoates (bearing multifunctional groups) as simple and useful starting materials is explored, thus cyclizing with an array of coupling partners to deliver a broad range of oxygen-, nitrogen-, sulfur-containing heterocycles alongside fused-, and spiro-heterocyclic compounds. In addition, these examples will also focus the scope and reaction limitations, as well as mechanistic investigations into the synthesis of these heterocycles. The biological significance will also be discussed, citing relevant examples of drug molecules highlighting each class of heterocycles. This review summarizes the recent developments in the synthetic methods for the synthesis of various heterocycles using alkynoates as readily available starting materials under transition-metal catalysis.

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

Synthesis of fused-tetrahydropyrimidines: one-pot methylenation–cyclization utilizing two molecules of CO2

A methylenation–cyclization reaction employing cyclic enaminones with primary aromatic amines and two molecules of CO₂ to furnish fused-tetrahydropyrimidines has been developed.

Controllable synthesis of pyrido[2,3-b]indol-4-ones or indolo[3,2-b]quinolines via formal intramolecular C(sp2)-H functionalization

A novel Fe-catalyzed protocol for the controllable synthesis of pyrido[2,3-b]indol-4-ones or indolo[3,2-b]quinolines has been developed by using indole-2-carboxylic derivatives as starting materials. Indole-2-carboxenamines were transformed into pyrido[2,3-b]indol-4-ones through intramolecular N-H/C-H coupling, in which a carbonyl 1,2-migration was involved. Whereas, when indole-2-carboxarylamines were employed, indolo[3,2-b]quinolones were produced through direct N-H/C-H coupling. The desired products were obtained under mild reaction conditions in moderate to good yields with wide substrate scope. The natural product quindolinone was conveniently prepared by this reaction.

In-Water Synthesis of 5-Thiolated 1,2,3-Triazoles from β-Thioenaminones by Diazo Transfer Reaction

The synthesis of 1,2,3-triazoles with a sulfur-based side chain has been accessed with the metal-free annulation reactions of readily available β-thiolated enaminones and tosyl hydrazine. By these reactions with water as the only medium, a broad array of 5-thiolated 1,2,3-triazoles have been synthesized with generally good to excellent yields. Except using TMEDA (N,N,N',N'-tetramethylethylenediamine) as the only base promoter, not any other catalyst or additive is required, thus providing an efficient and environmentally benign method for useful 1,2,3-triazole synthesis.

A co-operative effect of visible light photo-catalysis and CoFe2O4 nanoparticles for green synthesis of furans in water

A novel approach to poly-functionalized furan synthesis is disclosed via oxidative decarboxylative [3+2] cycloaddition using co-operative catalysis by visible light and CoFe₂O₄ nanoparticles.

The base-promoted synthesis of multisubstituted benzo[b][1,4]oxazepines

A variety of substituted benzo[b][1,4]oxazepines have been prepared via base-promoted intramolecular O-arylation from N-(2-haloaryl)enaminones under metal-free conditions.

Facile synthesis of substituted 3-aminofurans through a tandem reaction of N-sulfonyl-1,2,3-triazoles with propargyl alcohols

A relay catalysis strategy for substituted 3-aminofurans synthesis has been developed.