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Cercosporin-Photocatalyzed [4+1]- and [4+2]-Annulations of Azoalkenes Under Mild Conditions
Published on: July 17, 2020
Rhodium-Catalyzed [2+1+2+1] Cycloaddition of Benzoic Acids with Diynes through Decarboxylation and C≡C Triple Bond
Yusaku Honjo1, Yu Shibata1, Ken Tanaka1
1Department of Chemical Science and Engineering, Tokyo Institute of Technology, O-okayama, Meguro-ku, Tokyo, 152-8550, Japan.
Abstract:
It has been established that an electron-deficient cyclopentadienyl rhodium(III) (CpE RhIII ) 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 CpE RhIII 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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