Visible Light-Mediated C(sp²)–H Selenylation of Amino Pyrazole and Amino Uracils in the Presence of Rose Bengal as an Organophotocatalyst

Abstract

Herein, we report an efficient methodology for the synthesis of alkyl, benzyl, and phenyl selenoethers of aminopyrazoles and aminouracils by C­(sp2)–H functionalization in the presence of visible light and Rose Bengal as an organophotocatalyst. The reaction of amino pyrazole/iosothiazole/isoxazole or amino uracils with 0.5 equivalent of diphenyl/dibenzyl/diethyl diselenides in the presence of visible light in acetonitrile medium and a catalytic amount of Rose Bengal provided the corresponding phenyl, benzyl, or ethyl selenoethers in good to very good yields. We have also utilized some of the selenylated aminopyrazoles for the preparation of pyrazole-fused dihydropyrimidines tethered with arylselenoethers by a catalyst-free one-pot three-component reaction. The notable features of this methodology are metal-free reaction conditions, good to very good yields, use of an organic photocatalyst, and wide substrate scope; it is also applicable to gram-scale synthesis and provides selenoethers of medicinally important heterocycles such amio-pyrazole, isoxazole, isothiazole, and uracils.

Dimethyl Sulfoxide-Assisted, Iodine- and Ascorbic Acid-Catalyzed One-Pot Synthetic Approach for Constructing Highly Substituted Pyrazolo[1,5-a]quinoline Thioether Derivatives

“…After the one-pot condition (Scheme ) in our hand for the synthesis of 22a , different pyrazole amine 17 , , thiophenol 18 , and acetylene derivatives 19 were considered to explore the thiolation/[4 + 2] benzannulation reaction. As displayed in Scheme , we have identified that electron-donating substituents −Me and −OMe at the para position on 1-phenyl of pyrazole amine ( 17g and 17h ) afforded pleasing yields (61 and 63%) of the pyrazoloquinoline thioether compound ( 22g and 22h ) compared to halogen and electron-withdrawing substituents −Br ( 17b ), −Cl ( 17c ), −F ( 17d ), −CN ( 17e ), and −NO 2 ( 17f ), where the relative products ( 22b–22f ) were acquired in 46–56% yields, respectively (Scheme ).…”

“…The general procedure for the synthesis of compounds 17 : 3-phenyl pyrazole amine, 4-phenyl pyrazole amine, and pyrazole amine derivatives are synthesized according to the literature report. , Compounds 18 and 19 are commercially available.…”

Transition-Metal-Free Dehydrogenation of Benzyl Alcohol for C–C and C–N Bond Formation for the Synthesis of Pyrazolo[3,4-b]pyridine and Pyrazoline Derivatives

“…The dried crude reaction mass was subjected to column chromatography to provide the corresponding pyrazole amine 7a in a good yield. The general procedure was followed for the preparation of all other pyrazole amine compounds 7b–7m . , …”

Synthesis and Application Dichalcogenides as Radical Reagents with Photochemical Technology

“…In 2022, Choudhury et al [ 47 ] reported a visible-light-mediated C(sp 2 )−H selenation reaction of aminopyrazoles ( Scheme 17 ). The authors chose 5-amino-3-methyl-1 H -phenylpyrazoles 83 and diphenyl diselenides as model substrates and demonstrated experimentally that the reaction does not require additional metal oxidants; only 12 h of visible-light irradiation in nitrogen at room temperature is required to obtain the desired target products.…”