Phenanthroline-Decorated Covalent Organic Framework for Catalytic Synthesis of 2-Aminobenzothiazoles in Water

2-Aminobenzothiazoles are widely used in the fields of pharmaceuticals and pesticides. Herein, we report a metal-free protocol for the preparation of 2-aminobenzothiazoles by a covalent organic framework (COF) catalyzed tandem reaction. In the presence of catalytic amount of phenanthroline-decorated COF (Phen-COF), a variety of 2-aminobenzothiazoles are obtained in excellent yields by the cross-coupling of 2-iodoanilines with isothiocyanates at room temperature in water. In addition, the COF-catalyst is very stable and can be reused at least seven times without loss of its catalytic activity.

A Green Approach to 2-Substituted Benzo- and Naphthothiazoles via N-bromosuccinimide/Bromide-Mediated C(aryl)-S Bond Formation

2-Substituted benzo- and naphthothiazoles have been conveniently prepared from the intramolecular cyclization of phenylthioureas and activated thiobenzanilides or the coupling of isothiocyanates with amines under mild conditions using N-bromosuccinimide/tetrabutylammonium bromide in 1,2-dimethoxyethane (DME) under ambient conditions. The reactions produce moderate to excellent yields with good functional group tolerance and avoid the use of harsh thermal conditions, corrosive reagents, halogenated solvents, toxic metal salts, and expensive metal catalysts, and are amenable to preparations on a gram-scale.

DABCO-Catalyzed Reaction of 2-Naphthols with Aryl Isothiocyanates: Access to 2-Iminonaphtho-1,3-oxathioles

2-Naphthols 1 were found to react with aryl isothiocyanates 2 to provide 2-iminonaphtho-1,3-oxathioles 3 in the presence of DABCO as a catalyst. When elemental sulfur was used, moderate to good yields of 3 could be achieved from a nearly equimolar mixture of two starting materials 1 and 2. Products 3 could also be formed in the absence of sulfur or an external oxidant. In the latter case, an additional equivalent of 2 was found to act as a dehydrogenating agent.

Reactions of α-Phenylglyoxylic Acids with ortho-Functionalized Anilines in Deep Eutectic Solvents: Selective Syntheses of 3-Aryl-2H-benzo[b][1,4]oxazin-2-ones, 2-Arylbenzothiazoles, and 3-Arylquinoxalin-2(1H)-ones

α-Phenylglyoxylic acid is a novel cyclization reagent. In this study, three cyclization products were synthesized by the reaction of α-phenylglyoxylic acids with ortho-functionalized anilines in deep eutectic solvents (DES). The five-membered-ring-formation products, the 2-arylbenzothiazoles, with a highest yield of 88%, were obtained by the reaction between 0.30 mmol of an o-aminothiophenol and 0.30 mmol of an α-phenylglyoxylic acid in choline chloride (ChCl)/d-(–)-tartaric acid DES at 60 °C for 0.5 h. The six-membered-ring-formation products, 3-aryl-2H-benzo[b][1,4]oxazin-2-one derivatives, were obtained in yields up to 99% by the reaction between 0.30 mmol of an o-aminophenol and 0.60 mmol of an α-phenylglyoxylic acid in ChCl/urea DES at 80 °C for 2.0 h. In the reaction between 0.30 mmol of o-phenylenediamine and 0.45 mmol of an α-phenylglyoxylic acid in ChCl/anhydrous tin(II) chloride DES at 70 °C for 1.5 h, the six-membered-ring-formation products, 3-arylquinoxalin-2(1H)-one derivatives, were synthesized, with a highest yield of 96%. This cyclization reaction occurred without the addition of other catalysts, and the title compounds were obtained with good yields under mild conditions.

Engineering Metal-Organic Framework Catalysts for C-C and C-X Coupling Reactions: Advances in Reticular Approaches from 2014-2018

Metal-organic frameworks (MOFs) are a class of crystalline porous materials that have been actively used for several industrial and synthetic applications. MOFs are spatially and geometrically extrapolated coordination polymers with intriguing properties such as tunable porosity and dimensionality. In terms of their catalytic efficiency, MOFs combine the easy recoverability of heterogeneous catalysts with the increased selectivity of biological catalysts. It is therefore not surprising that a lot of work on optimizing MOF catalysts for organic transformations has been carried out over the past decade. In this review, recent developments in MOF catalysis are summarized, with special attention being paid to C-C, C-N, and C-O coupling reactions. The influence of pore size, pore environment, and load on catalytic activity is described. Post-synthetic stabilization techniques and host-guest interactions in caged MOF scaffolds are detailed. Mechanistic aspects pertaining to the use of MOFs in asymmetric heterogeneous catalysis are highlighted and categorized.

DMSO-mediated palladium-catalyzed cyclization of two isothiocyanates via C–H sulfurization: a new route to 2-aminobenzothiazoles

DMSO was found to activate arylisothiocyanates for self-nucleophilic addition. A subsequent intramolecular C–H sulfurization catalyzed by PdBr₂ enables access to a wide range of 2-aminobenzothiazole derivatives in moderate to good yields. This is the first example of a DMSO-mediated Pd-catalyzed synthesis of 2-aminobenzothiazoles through cyclization/C–H sulfurization of two isothiocyanates.

DMSO-initiated coupling of two isothiocyanates; Pd-catalyzed C–H sulfurization.

A metal-free synthesis of 2-aminobenzothiazoles through aminyl radical addition to aryl isothiocyanates

A convenient synthesis of 2-aminobenzothiazoles, starting from aryl isothiocyanates and formamides under metal-free conditions, is described. Various secondary and tertiary amine- and even α-amino acid-derived formamides can be used as amino sources in this process. Mechanistic studies suggest that the reaction is initiated by decarbonylative aminyl radical formation in the presence of n-Bu4NI and TBHP, followed by aminyl radical addition to isothiocyanates and cyclization via sulfur centred radical intermediates.

Tunable Prussian blue analogues for the selective synthesis of propargylamines through A3 coupling

M¹[Co(CN)₆]_2/3-type Prussian blue analogues (M¹–Co PBAs) were studied as catalysts for the synthesis of propargylamines via A³ coupling of phenylacetylene, benzaldehyde and piperidine.

Catalytic Organic Reactions in Water toward Sustainable Society

Traditional organic synthesis relies heavily on organic solvents for a multitude of tasks, including dissolving the components and facilitating chemical reactions, because many reagents and reactive species are incompatible or immiscible with water. Given that they are used in vast quantities as compared to reactants, solvents have been the focus of environmental concerns. Along with reducing the environmental impact of organic synthesis, the use of water as a reaction medium also benefits chemical processes by simplifying operations, allowing mild reaction conditions, and sometimes delivering unforeseen reactivities and selectivities. After the "watershed" in organic synthesis revealed the importance of water, the development of water-compatible catalysts has flourished, triggering a quantum leap in water-centered organic synthesis. Given that organic compounds are typically practically insoluble in water, simple extractive workup can readily separate a water-soluble homogeneous catalyst as an aqueous solution from a product that is soluble in organic solvents. In contrast, the use of heterogeneous catalysts facilitates catalyst recycling by allowing simple centrifugation and filtration methods to be used. This Review addresses advances over the past decade in catalytic reactions using water as a reaction medium.

Metal-Free Synthesis of 2-Aminobenzothiazoles via Iodine-Catalyzed and Oxygen-Promoted Cascade Reactions of Isothiocyanatobenzenes with Amines

In this paper, a highly efficient and sustainable synthesis of 2-aminobenzothiazoles through the cascade reactions of isothiocyanatobenzenes with primary or secondary amines by using iodine as a catalyst and oxygen as an oxidant is presented. Mechanistically, the formation of the title compounds involves the in situ formation of the required benzothiourea intermediate followed by its intramolecular cross dehydrogenative coupling of a C(sp²)-H bond and a S-H bond. To our knowledge, this should be the first example in which 2-aminobenzothiazoles are efficiently prepared from simple and cheap isothiocyanates and amines under metal-free conditions by using iodine as a catalyst and molecular oxygen as an oxidant with water as the byproduct. Compared with literature protocols, this method eliminates the use of ortho-halo-substituted precursors, expensive transition-metal catalysts, and hazardous oxidants.

Aerobic Copper-Mediated Domino Three-Component Approach to 2-Aminobenzothiazole Derivatives

An unprecedented three-component reaction involving a 2,2'-diaminodiaryl disulfide, copper cyanide, and an electrophile is described. This transformation is based on an oxidative copper-mediated S-cyanation as a key step and involves a cyanation/cyclization/acylation domino sequence enabling a rapid and efficient synthesis of diversely substituted 2-aminobenzothiazole derivatives. Notably, this reaction proceeds via an original mechanism involving an intermolecular migration of the acyl group.

Synthesis of 1,3,5-triazines via Cu(OAc)2-catalyzed aerobic oxidative coupling of alcohols and amidine hydrochlorides

Cu(OAc)2 was found to be an efficient catalyst for dehydrogenative synthesis of 1,3,5-triazine derivatives via oxidative coupling reaction of amidine hydrochlorides and alcohols in air. Both aromatic and aliphatic alcohols can be involved in the reaction and thirty-three products were obtained with good to excellent yields. Moreover, the use of a ligand, strong base and organic oxidant is unnecessary.

Iodine-catalyzed formation of substituted 2-aminobenzothiazole derivatives in PEG400

An iodine-catalyzed formation of substituted 2-aminobenzothiazole derivatives is herein described using hydrogen peroxide as an oxidant in PEG₄₀₀.

Direct construction of 2-alkylbenzo-1,3-azoles via C–H activation of alkanes for C–C and C–X (X = O, S) bond formation

2-Alkylated benzo(oxa)thiazoles were prepared directly from simple alkanes and aryl isocyanates/isothiocyanates in a one-pot procedure.

Mild Cu(OAc)2·H2O-catalyzed synthesis of multi-substituted 1,2,4-triazoles from amidines with nitriles via a N–N/C–N coupling

Multi-substituted 1,2,4-triazoles were obtained via a Cu(OAc)₂·H₂O-catalyzed aerobic oxidation of amidines with nitriles.