[Omim]Cl/FeCl 3 -catalyzed cross-dehydrogenative-coupling of 1,4-benzoxazinones with various indoles
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ORIGINAL PAPER
[Omim]Cl/FeCl3‑catalyzed cross‑dehydrogenative‑coupling of 1,4‑benzoxazinones with various indoles Ali Sharifi1 · Maryam Moazami1 · M. Saeed Abaee1 · Mojtaba Mirzaei1 Received: 30 October 2019 / Accepted: 22 April 2020 © Iranian Chemical Society 2020
Abstract A novel C(sp3)–C(sp2) cross-dehydrogenative-coupling procedure was developed for the reaction of benzoxazin-2-ones with indole derivatives. Thus, ionic liquid-mediated coupling of 1,4-benzoxazinone derivatives with indoles were observed in which [Omim]Cl/FeCl3 acted as both the solvent and the catalyst. Under [Omim]Cl/FeCl3-TBHP conditions, derivatives of 1 coupled at room temperature with indoles bearing various substituents to give the target products in good yields and within 0.5–2 h time period. The procedure is relatively environmentally friendly and is applicable to several derivatives of both reactants to access the desired products. Keywords Ionic liquids · CDC reactions · Benzoxazinones · Heterocycles
Introduction Carbon–carbon (C–C) and carbon–heteroatom (C–X) bond formations are of fundamental reactions and are among the most important processes in synthetic organic chemistry to quickly build up complex molecules from simpler reactants [1]. In this context, direct coupling of C–H bonds with other C–H or X–H bonds via cross-dehydrogenative-coupling (CDC) reactions provides a useful route to form C–C or C–X bonds to construct various target molecules, where X would be heteroatoms such as oxygen, sulfur or nitrogen [2–6]. A major advantage achieved by direct CDC reactions is that the introductory steps for the preparation of reactants containing carbon-leaving groups and carbon–metal bonds are avoided [7–10]. In addition, CDC reactions are very useful methods for oxidation of amines [11–14]. This is because the undesired in situ oxidation of the starting amines to their respective iminium ions is avoided. Therefore, addition of nucleophiles of choice to the intermediate iminium to access Electronic supplementary material The online version of this article (https://doi.org/10.1007/s13738-020-01941-y) contains supplementary material, which is available to authorized users. * Ali Sharifi [email protected] 1
Faculty of Organic Chemistry and Natural Products, Chemistry and Chemical Engineering Research Center of Iran, Pajohesh Blvrd., Tehran 1496813151, Iran
the desired final structures is facilitated [15–17]. As a consequence of this strategy, several natural products and biologically active compounds have been synthesized so far [18]. Many biologically active compounds are known which have 1,4-benzoxazinone skeleton in their structure [19–22]. 1,4-Benzoxazinone are also synthetically manipulated to access more complex molecules with desired pharmaceutical properties [18, 23]. Some related illustrative examples are presented in Fig. 1. These chemical transformations are usually performed through derivatization of the carbon atom next to the amine functional group in the benzoxazinone ring. Despite the efficiency of this met
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