General Procedure D. To a solution of ethyl1-benzyl-3-formyl-2-isopropyl-1H-indole-6-carboxylate (Compound 35, 220 mg, 0.63 mmol) in t-BuOH (6 ml), CH3CN (1 ml), and 2-methyl-2-butene (1.76 ml) was added a solution of NaH2PO4 (1.51 g, 12.6 mmol) and NaClO2 (80%, 1.13 g, 12.6 mmol) in H2O (6 ml). The mixture was stirred at room temperature fro 12 h. The reaction mixture was extracted with EtOAc (×3) and the combined organic layer was washed with brine, dried over Na2SO4, and concentrated in vacuo. The residue was purified by chromatography on silica gel (0→20% EtOAc-hexanes) to yield the title compound as a yellow solid.
