SmI(2)-promoted radical addition reactions with N-(2-Indolylacyl)oxazolidinones: synthesis of bisindole compounds |
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Authors: | Lindsay Karl B Ferrando Francesc Christensen Kasper L Overgaard Jacob Roca Tomàs Bennasar M-Lluïsa Skrydstrup Troels |
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Institution: | Center for Insoluble Protein Structures, Department of Chemistry and Interdisciplinary Nanoscience Center, University of Aarhus, Langelandsgade 140, 8000 Aarhus C, Denmark. |
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Abstract: | The treatment of N-acyl oxazolidinones of N-benzyl 2-indolecarboxylic acids varying in the substitution pattern of the indole ring with samarium diiodide at -78 degrees C led to the formation of two indole dimer products. The major product isolated in yields from 55 to 59% represents an unsymmetrical dimer arising from 1,4-addition to the 2-indolecarboxylic acid derivative of a possible ketyl-type radical anion intermediate originating from the reduction of the exocyclic carbonyl group of the N-acyl oxazolidinone. The minor dimer, represented by a symmetrical diketone, was produced in yields ranging from 11 to 23%. Even in the presence of an alpha,beta-unsaturated amide, dimerization was the preferred pathway rather than the formation of a gamma-keto amide. Upon treatment with acid, the unsymmetrical indole dimer cyclized to form a diindolequinone. Finally, the N-acyl oxazolidinones of pyrrole-2-carboxylic acid and 3-indolecarboxylic acid preferred in both cases to undergo C-C bond formation with an acrylamide in the presence of SmI2 rather than dimerization. |
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