Solvent-Free Heterocyclic Synthesis

Calcium-Based Sustainable Chemical Technologies for Total Carbon Recycling

Calcium carbide, a stable solid compound composed of two atoms of carbon and one of calcium, has proven its effectiveness in chemical synthesis, due to the safety and convenience of handling the C≡C acetylenic units. The areas of CaC₂ application are very diverse, and the development of calcium-mediated approaches resolves several important challenges. This Review aims to discuss the laboratory chemistry of calcium carbide, and to go beyond its frontiers to organic synthesis, life sciences, materials and construction, carbon dioxide capturing, alloy manufacturing, and agriculture. The recyclability of calcium carbide and the availability of large-scale industrial production facilities, as well as the future possibility of fossil-resource-independent manufacturing, position this compound as a key chemical platform for sustainable development. Easy regeneration and reuse of the carbide highlight calcium-based sustainable chemical technologies as promising instruments for total carbon recycling.

Cu-Catalyzed carbamoylation versus amination of quinoline N-oxide with formamides

Carbamoylation and amination of quinoline with formamides was developed via copper-catalyzed C–C and C–N bond formations.

Highly enantioselective addition of sulfur-containing heterocycles to isatin-derived ketimines

In this study, we report a highly stereoselective addition of sulfur-containing heterocyclic compounds to isatin-derived ketimines efficiently catalyzed by cinchonidine-derived bifunctional tertiary aminothiourea (1 mol%).

Solvent-free incorporation of CO2 into 2-oxazolidinones: a review

This review is an attempt to give an overview on the recent advances and developments in the synthesis of 2-oxazolidinone frameworks through carbon dioxide (CO₂) fixation reactions under solvent-free conditions. The cycloaddition of CO₂ to aziridine derivatives is discussed first. This is followed by carboxylative cyclization of N-propargylamines with CO₂ and three-component coupling of epoxides, amines, and CO₂. Finally, cycloaddition of CO₂ to propargylic alcohols and amines will be covered at the end of the review. The literature has been surveyed up until the end of 2018.

This review is an overview on the recent advances in the synthesis of 2-oxazolidinones through CO₂ fixation reactions under solvent-free conditions.

Fe(III)-Catalyzed Bicyclization of Yne-Allenones With Indoles for the Atom-Economic Synthesis of 3-Indolyl Cyclobutarenes

A new Fe(III)-catalyzed bicyclization reaction of yne-allenones with indoles has been established, enabling the direct construction of cyclobuta[a]naphthalen-4-ols with an all-carbon quaternary center in good to excellent yields. This reaction was performed by using low-cost FeCl3 as the catalyst and EtOH as the environmentally benign solvent, providing a green protocol for constructing the cyclobutarene framework with a high degree of atom economy and functional group compatibility. The reaction mechanism was proposed to proceed through a [2 + 2] cycloaddition/1,6-conjugate addition cascade.

TEMPO-Catalyzed Direct Conversion of Primary Alcohols to α-Chloroacetals with TCCA Both as an Oxidant and a Chlorination Reagent

Multistep reactions are often required for the transformation of alcohols to α-chloroacetals via the unstable intermediates aldehydes or α-halo aldehydes. Herein, we report a simplified procedure for practical synthesis of α-chloroacetals using 2,2,6,6-tetramethylpiperidine-1-oxyl as a catalyst and trichloroisocyanuric acid both as an oxidant and a chlorination reagent. The reaction is one-pot, solvent-free and high-yielding. In addition, the α-chloroacetals have been transformed to enol ethers through the elimination reaction in the presence of sodium.

Efficient Synthesis of Five Types of Heterocyclic Compounds via Intramolecular Elimination Using Ultrasound-Static Heating Technique

An experimental technique, ultrasound-static heating, has been developed for the efficient synthesis of heterocyclic compounds. The technique involves ultrasonic irradiation and static heating processes. First, the ultrasonic irradiation process is performed to form an intermediate of the heterocyclic compound under mild conditions and the subsequent static heating process (heating the intermediate under solvent-free conditions without stirring) produces the target heterocyclic compounds via intramolecular elimination.

Palladium-Catalyzed Regioselective Alkoxylation via C-H Bond Activation in the Dihydrobenzo[c]acridine Series

5,6-Dihydrobenzo[c]acridine belongs to the large aza-polycyclic compound family. Such molecules are not fully planar due to the presence of a partially hydrogenated ring. This paper describes the first Pd-catalyzed alkoxylation via C-H bond activation of variously substituted 5,6-dihydrobenzo[c]acridines. We determined suitable conditions to promote the selective formation of C-O bonds using 10% Pd(OAc)2, PhI(OAc)2 (2 eq.) and MeOH as the best combination of oxidant and solvent, respectively. Under these conditions, 5,6-dihydrobenzo[c]acridines bearing substituents at both rings A and D were successfully functionalized, giving access to polysubstitutited acridine motifs.

Molecular iodine as a mild catalyst for cross-coupling of alkenes and alcohols

C–C bond formation is one of the most fundamental approaches toward molecular diversity in organic synthesis. In pursuit of environmentally friendlier chemical approaches to organic chemistry, we present a new metal-free method for direct dehydrative cross-coupling of alcohols and alkenes using molecular iodine as a Lewis acid catalyst under solvent-free reaction conditions. The reaction is atom-economical, tolerant to air and allows simple synthetic procedure, furnishing Csp 3–Csp 2 coupling products with yields up to 97%. The method has proved efficient for coupling of secondary benzyl alcohols with phenyl-substituted alkenes.

Synthesis of thieno[2,3-c]acridine and furo[2,3-c]acridine derivatives via an iodocyclization reaction and their fluorescence properties and DFT mechanistic studies

In this paper, we report the novel synthesis of thieno[2,3-c]acridine and furo[2,3-c]acridine derivatives via intramolecular iodocyclization reaction. The thieno[2,3-c]acridine derivatives exhibited blue fluorescence in hexane.

Solvent and catalyst free ring expansion of indoles: a simple synthesis of highly functionalized benzazepines

Highly functionalized benzazepines have been synthesized from indoles via ring expansion. Ring contraction of benzazepines to indole derivatives has also been acheived in excellent yields.

Direct thiolation of aza-heteroaromatic N-oxides with disulfides via copper-catalyzed regioselective C–H bond activation

A novel and efficient thiolation reaction of aza-heteroaromatic N-oxides with disulfides via copper catalyzed C–H activation has been developed.

Brønsted acid catalysed eco friendly synthesis of quaternary centred C-3 functionalized oxindole derivatives

A facile atom economic and eco friendly protocol for the synthesis of biologically important quaternary centered C-3 functionalized oxindole derivatives, with a novel nucleus, in high yields has been demonstrated.