Regioselective oxidation of indoles to 2-oxindoles
Santosh V Shelar1, Narshinha P Argade1
1Division of Organic Chemistry, National Chemical Laboratory (CSIR), Pune 411 008, India. np.argade@ncl.res.in and Academy of Scientific and Innovative Research (AcSIR), New Delhi 110 025, India.
Abstract:
Facile regioselective oxidation of indoles to 2-oxindoles promoted by sulfuric acid adsorbed on silica gel is reported. The demonstrated practical site-selective heterogeneous oxidation reactions conveniently take place with a broad substrate scope and functional group tolerances. The present oxidation strategy is also employed to accomplish the total synthesis of natural products donaxaridine and donaxarine. On the basis of analytical and spectral data it is evidenced that donaxarine stays in equilibrium with its hydrated ring opened form. The structural features essential for this type of oxidation and plausible mechanism are discussed in brief.
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