A mixture of 5-hydroxy-2,3-dihydro-indole-1-carboxylic acid tert-butyl ester (0.6 g, 2.6 mmol) in tert-butyl alcohol (8 ml) and 2-butanone (4 mL) was added cesium carbonate (2.5 g, 7.7 mmol) followed by methanesulfonic acid 4-tert-butyl-cyclohexyl ester (1.9 g, 7.7 mmol). The mixture was heated in a sealed vial at 100° C. over night to form precipitate. The mixture was treated with dichloromethane and the precipitate was filtered off and the solvent was concentrated. The residue was purified with a silica gel column eluted with ethyl acetate in hexanes from 0 to 30% to give precipitate (0.96 g, yield: 100%). ESI-MS: 373.30 (M)+.
