Methylsulfonic Acid Adsorbed on Silica Gel as a Solid Acid for Dimerization of Indoles: A Convenient Synthesis of 2,3′-Bi(3<i>H</i>-indol)-3-one Oximes
A simple, convenient, and efficient approach for the synthesis of (E)-2,3-bi(3H-indol)-3-one oxime derivatives has been developed. The methodology is based on a three-component coupling reaction of indoles and sodium nitrite using a silica-supported methylsulfonic acid as solid acid. The practical utility of this three-component coupling reaction has been demonstrated in the gram-scale dimerization of indole. [Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications (R) for the following free supplemental resource: Full experimental and spectral details.]