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Synlett 2011(14): 2075-2079  
DOI: 10.1055/s-0030-1260981
LETTER
© Georg Thieme Verlag Stuttgart ˙ New York

Ir(III)-Catalyzed Room-Temperature Synthesis of Multisubstituted Benzofurans Initiated by C-H Activation of α-Aryloxy Ketones

Takanori Shibata*a, Yu-ki Hashimotoa, Maiko Otsukaa, Kyoji Tsuchikamaa, Kohei Endob
a Department of Chemistry and Biochemistry, School of Advanced Science and Engineering, Waseda University, Okubo, Shinjuku, Tokyo, 169-8555, Japan
Fax: +81(3)52868098; e-Mail: tshibata@waseda.jp;
b Waseda Institute for Advanced Study, Shinjuku, Tokyo, 169-8050, Japan
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Publikationsverlauf

Received 9 May 2011
Publikationsdatum:
03. August 2011 (online)

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Abstract

Cyclodehydration of various α-aryloxy ketones proceeded to give various multisubstituted benzofurans by using an Ir(III) catalyst, which was prepared from [Cp*IrCl2]2, AgSbF6, and Cu(OAc)2. The use of the cationic iridium complex with a carboxylate salt realized the efficient transformation at ambient temperature.

Key words

C-H activation - benzofurans - cyclodehydration - iridium - room temperature

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6

We already excluded a Friedel-Crafts mechanism by competitive experiment of 4-(3-acetylphenyl)butan-2-one (1a) and 4-(3-methoxyphenyl)butan-2-one, see Supporting Information of ref. 4 in detail.

12

Other silver salts, such as AgOTf and AgBF4, gave poorer results than AgSbF6.

13

Iridium dicarboxylate complex, which was prepared from [Cp*IrCl2]2 (5 mol% Ir), AgSbF6 (10 mol%), and KOPiv (10 mol%), had almost no catalytic activity.

15

The reaction of 4-(3-acetylphenyl)butan-2-one or
1-(3-acetyl­phenylamino)propan-2-one did not proceed under the same reaction conditions.