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SmI 2 -Promoted Radical Addition Reactions with N -(2-Indolylacyl)oxazolidinones: Synthesis of Bisindole Compounds

2007; American Chemical Society; Volume: 72; Issue: 11 Linguagem: Inglês

10.1021/jo070273d

1520-6904

Karl B. Lindsay, Francesc Ferrando, Kasper L. Christensen, Jacob Overgaard, Tomàs Roca, M.‐Lluïsa Bennasar, Troels Skrydstrup,

Free Radicals and Antioxidants

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 °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 α,β-unsaturated amide, dimerization was the preferred pathway rather than the formation of a γ-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.