Due to the versatile applications of thioethers and thioesters in organic synthesis, medicinal chemistry, the pharmaceutical industry, and materials science, recently the construction of C-S bonds has emerged as the forefront in the field of cross-coupling reactions. Enough progress has been made in this direction by using both metal catalysis and other alternative processes. A brief review of the recent developments in the area of C-S coupling reaction is described.
A simple and an efficient one-pot three-component reaction of arylamines, aromatic aldehydes, and cyclic ketones was described for the synthesis of various fused quinoline, benzoquinoline, and naphthoquinoline derivatives by using camphorsulfonic acid as a catalyst. The exploitation of pregnenolone steroid for benzoquinolines and terephthalaldehyde for bis-benzoquinolines synthesis was achieved with 68-75% yields. The reactivity of arylamines and the mechanistic study for the formation of benzoquinoline was described precisely. The present protocol offers a great potential for atom-economy under mild conditions.
An example of proaromatic C(alkenyl)−H olefination is reported. This protocol utilized a free carboxylic acid as a directing group for C(alkenyl)−H activation of 1,4-cyclohexadiene and coupled with various alkenes. Direct and sequential bisolefinations of proaromatic acids were achieved. The synthetic applicability has been exhibited by [4 + 2] cycloaddition and decarboxylative aromatization of the resulting proaromatic 1,3dienes. Additionally, several kinetic studies also have been carried out to elucidate the reaction mechanism.
In this study, a general procedure was proposed for synthesizing thioethers and selenide ethers from anilines under solventfree and transition-metal-free conditions. Thioethers were formed when anilines reacted with thiols under blue light-emitting-diode (LED) irradiation at room temperature without a photocatalyst. When reactions were performed using anilines and diselenides, the corresponding selenide ethers were obtained with satisfactory to excellent yields. The reaction was performed under photocatalyst-free and solvent-free conditions without blue LEDs. The advantages of this system include convenient operations, mild reaction conditions, satisfactory functional group tolerance, and late-stage selenylation of drug molecules.
A nickel-catalyzed
aryl–aroyloxyl C(sp2)–O
radical cross-coupling reaction conducted using a redox active ester
with aryl zinc reagent was developed. This method demonstrates a new
disconnection approach for formation of aryl aryl esters. In the one-pot
sequential process, the readily available aryl carboxylic acids can
be converted into functionalized aryl aryl esters and heteroaryl esters.
This protocol is amenable to the gram-scale synthesis. The present
method has a wide substrate scope and high functional group tolerance.
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