Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond Cleavage |
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Authors: | Yusaku Honjo Dr Yu Shibata Prof Dr Ken Tanaka |
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Institution: | Department of Chemical Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8550 Japan |
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Abstract: | It has been established that an electron-deficient cyclopentadienyl rhodium(III) (CpERhIII) complex catalyzes the oxidative and decarboxylative 2+1+2+1] cycloaddition of benzoic acids with diynes through C≡C triple bond cleavage, leading to fused naphthalenes. This cyclotrimerization is initiated by directed ortho C−H bond cleavage of a benzoic acid, and the subsequent regioselective alkyne insertion and decarboxylation produce a five-membered rhodacycle. The electron-deficient nature of the CpERhIII complex promotes reductive elimination giving a cyclobutadiene–rhodium(I) complex rather than the second intermolecular alkyne insertion. The oxidative addition of the thus generated cyclobutadiene to rhodium(I) (formal C≡C triple bond cleavage) followed by the second intramolecular alkyne insertion and reductive elimination give the corresponding 2+1+2+1] cycloaddition product. The synthetic utility of the present 2+1+2+1] cycloaddition was demonstrated in the facile synthesis of a donor–acceptor 5]helicene and a hemi-hexabenzocoronene by a combination with the chemoselective Scholl reaction. |
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Keywords: | C≡C cleavage C−H functionalization cycloaddition decarboxylation rhodium complexes |
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