Synthesis and characterisation of copper(I) complexes with relevance to intramolecular Ullmann O,S-arylation

Copper-catalysed intramolecular Ullman arylation has been frequently used to synthesise benzoxazoles and benzothiazoles. Despite widespread use, investigations into the mechanism and speciation of copper-containing complexes relevant to the catalytic pathway have remained relatively limited. Accordingly, this study aims to elucidate the structural details of potential copper(I) intermediates through the analysis of their solid-state structures using X-ray crystallography, while also investigating the reactivities of these complexes. Five novel copper complexes are reported which are formed prior to the aryl halide activation step and feature distinct aggregation modes based on either Cu4N4O4C4 or Cu4N4S4C4 clusters.

An efficient metal free synthesis of 2-aminobenzothiozoles - a greener approach

A facile one-pot, metal-free method for the synthesis of 2-aminobenzothiazoles was developed, which includes an initial reaction of electron-deficient 2-haloanilines with aromatic isothiocyanates and the subsequent intramolecular cyclization of the resulting thioureas through the SNAr mechanism. This one-pot, atom-economical, robust, and scalable method avoids the use of reagents such as acid chlorides and Lawesson's reagent that are difficult to handle.

Copper-Catalyzed Ultrasonic-Promoted Coupling of Acetylene Analogs, Dialkyl azo dicarboxylate, and Benzazoles to Assemble Tricyclic Fused- Ring [1,2,3]triazolo[3,4-b][1,3]benzazole Analogs

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An unprecedented copper-catalyzed reaction of acetylene analogs with dialkyl azo dicarboxylate and benzazole analogs via a cross-coupling sequence was reported. A library of triazolobenzazole fused ring systems including [1,2,3] triazolo [3,4-b] [1,3] benzothiazole, [1,2,3] triazolo [3,4-b] [1,3] benzoxazole and [1,2,3] triazolo[3,4-b][1,3]benzimidazole structures were obtained in moderate to excellent yields under very mild reaction conditions. Structural confirmation of the final products became possible using different methods like spectroscopy and elemental analysis. The control experiments indicated C-H activation of acetylene by copper salts, followed by cycloaddition between a 2-(phenylethynyl)benzo[d]azol-3(2H)-yl anion and azo dicarboxylate as the key mechanistic feature. The broad substrate scope with simple and easily affordable starting materials, as well as mild reaction conditions are the noticeable attributes of this methodology, which provides facile access to the desired products.

Efficient Pd(ii)-catalyzed regioselective ortho-halogenation of arylcyanamides

2-Halo arylcyanamides have been constructed from cyanamides via Pd(ii)-catalyzed selective ortho-halogenation under moderate reaction conditions.

Isatin as a 2-aminobenzaldehyde surrogate: transition metal-free efficient synthesis of 2-(2'-aminophenyl)benzothiazole derivatives

A transition metal-free, convenient, and efficient practical approach has been devised for the synthesis of substituted 2-(2'-aminophenyl)benzothiazoles via a sulfur insertion strategy using isatin derivatives as 2-aminobenzaldehyde surrogates. KI assisted one-pot operation of isatin, arylamines and elemental sulfur resulted in the formation of a C-N and two C-S bonds and cascade cleavage of the isatin ring resulting in the formation of 2-(2'-aminophenyl)benzothiazoles. The significant features of this strategy are the readily available and inexpensive starting materials, broad substrate scope, sustainable reaction conditions and high yield of products. Importantly, the strategy was found to be appropriate for gram scale synthesis (>10 g) of 2-(2'-aminophenyl)benzothiazole derivatives. Moreover, the excellent photophysical properties (ΦF up to 60%) of 2-(2'-aminophenyl)benzothiazole derivatives provide huge scope in materials science.

Copper-Promoted One-Pot Approach: Synthesis of Benzimidazoles

A facile, one-pot, and proficient method was developed for the production of various 2-arylaminobenzimidazoles. This methodology is based for the first time on a copper catalyst promoted domino C-N cross-coupling reaction for the generation of 2-arylaminobenzimidazoles. Mechanistic investigations revealed that the synthetic pathway involves a copper-based desulphurization/nucleophilic substitution and a subsequent domino intra and intermolecular C-N cross-coupling reactions. Some of the issues typically encountered during the synthesis of 2-arylaminobezimidazoles, including the use of expensive catalytic systems and the low reactivity of bromo precursors, were addressed using this newly developed copper-catalyzed method. The reaction procedure is simple, generally with excellent substrate tolerance, and provides good to high yields of the desired products.

Ligand-controlled palladium catalysis enables switch between mono- and di-arylation of primary aromatic amines with 2-halobenzothiazoles

Mono- and di-arylation was switchable simply by varying the applied ligand from Xantphos to a pyridine-functionalized N-heterocyclic carbene (NHC) ligand.

Iodine-catalyzed guanylation of amines withN,N′-di-Boc-thiourea

Iodine-catalyzed guanylation of amines withN,N′-di-Boc-thiourea is especially useful for both electronically and sterically deactivated primary anilines.