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عنوان فارسی مقاله:
روش جدید اقتصادی اتم پالادیوم کاتالیز شده برای بنزوتیازول و بنزوکسازول با triarylbismuth از طریق فعال سازی CH
عنوان انگلیسی مقاله:
Atom economic palladium catalyzed novel approach for arylation of benzothiazole and benzoxazole with triarylbismuth reagents via C\\H activation
سال انتشار : 2016
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مقدمه انگلیسی مقاله:
1. Introduction
Transition-metal-catalyzed direct functionalization of C\\H bonds represents a powerful approach for the development of more sustainable chemical processes [1]. Direct arylation of arenes is an attractive alternative to traditional cross-coupling reactions [2]. These arylation reactions of benzothiazoles and benzoxazoles achieve regioselectivity using transition metal catalysts [3–6]. These moieties are part of compounds having several biological properties such as antibacterial, antitumor and anti-inflammatory [7–9]. The synthesis of such heterocycles and their derivatives has been a topic of research as they have important applications in a variety of fields. Transition metal catalyzed C\\H functionalization reactions of arenes and hetero arenes have gained more attention in the preparation of various organic and biologically important scaffolds [10]. A variety of aryl sources, such as aryl halides [11], arylboronic acids [12], iodobenzenediacetate [13], arenediazonium salts [14], aryl sulfamates [15], aryltrimethylammonium triflates [16], arene benzenesulfonyl chlorides [17] and substituted benzoic acids [18] have been used for the arylation of benzothiazoles and benzoxazoles. Some examples are given in Fig. 1. We have used triarylbismuthines as the arylating agent for the direct C\\H functionalization of benzothiazole and benzoxazole. Triarylbismuth compounds are stable, have low toxicity and can be easily prepared from aryl Grignard or lithium reagents and BiX3 inorganic salts [19,20]. The major advantage of triarylbismuth compounds is the low Bi\\C dissociation energy [21]. They also offer threefold coupling reactivity with other coupling partners under palladium catalyzed conditions [22]. They show various applications in organic transformations, either as reagents or catalysts [23]. Triarylbismuthines show various applications such as synthesis of unsymmetrical diaryl selenides [24], various arylation reactions [25, 26], C\\P bond formation [27] and cross-coupling with bromopyridines and bromoquinolines [28]. Organobismuth reagents are also used in Sarylation of diaryldisulfides [29], N-arylation of amines [30], azoles [31] and N-cyclopropylation of cyclic amides [32]. They also find important applications in O-arylation of N-protected 1,2-aminoalcohols [33], phenols [34], and in the synthesis of α-diimines from isocyanides [35]. To the best of our knowledge, this is the first report on the application of triarylbismuth as the arylating agent for the synthesis of benzothiazoles and benzoxazoles by C\\H activation. Here, we developed a PdCl2-Cu(OAc)2-PPh3 catalytic system for the arylation of benzothiazole and benzoxazole using triarylbismuth as the arylating agent.
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