| 研究実績の概要 |
We discovered that commercially available Fe(III) salt in combination with diphosphine ligand catalyzed direct twofold C-H activation/cross-coupling between heteroarene and (hetero)arene carboxamide bearing a 8-quinolinyl amide directing group in the presence of cheap dichloroalkane oxidant under mild condition. The iron-catalyst for twofold C-H activation/cross-coupling reaction is not only in advantage of its sustainability and low toxicity but also features remarkable chemo and regioselectivity to allow fully regioselective cross-coupling of thiophene derivatives using low ratio of two C-H substrates (1.0-1.2/1). Conjugated thiophene derivatives of optoelectronic material interest can be directly arylated using arene carboxamide in excellent yields to facilitate synthesis of carbon-bridged pi-functional materials. Mechanistic investigation reveals unique mechanistic feature accounts for the high chemoselectivity, which are 1) twofold C-H activation takes place on iron(III) thorough sequential σ-bond metathesis and 2) carboxamide substrate works as a proton shuttle to transfer proton of heteroarene to organozinc base to activate heteroaromatic substrates. The results described herein represent a new type of iron-catalyzed C-H activation reaction that avoids the use of any prefunctionalized coupling partners. The mechanistic understanding obtained from this research provides useful information to guide further development of iron-catalyzed C-H activation reactions obviating the usage of prefunctionalized couplings partners.
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