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Spiro-pyrrolidinyl-2-oxindoles were prepared by the oxidative rearrangement of N-acetyl1,2,3,4-tetrahydro-β-carbolines (THBC) using dimethyldioxirane generated in situ. The Nacetyl THBC substrates were obtained by Pictet-Spengler and acyl-Pictet-Spengler reactions of L-tryptophan methyl ester, followed by N-acetylation. The stereoselectivity of the oxidative rearrangement was evaluated and 2D nuclear magnetic resonance (NMR) was used to determine the stereochemistry of the oxindole products relative to L-tryptophan. Density functional theory calculations were consistent with a face selective, substrate controlled, epoxidation of the indolic double bond. The calculations indicated that the resulting epoxide would readily rearrange at room temperature via a concerted ring opening/ring contraction process to give the 3-substituted2-oxindole.

Synthesis of Spiro-Pyrrolidinyloxindoles by Oxidative Rearrangement of N-Acyltetrahydro-β-carbolines Using an Oxone/Aqueous Acetone Mixture