To 2,3-dihydro-1H-indole-3-carboxylic acid (A) (3.59 g, 22.0 mmol) was added aqueous N,N-dimethylformamide (DMF) (3:2 v/v; 75 cm3), and then N,N-diisopropylethylamine (9.0 cm3, 50.7 mmol). The mixture was stirred at room temperature for 5 min, before 4-methoxy-1-naphthyl sulfonyl chloride (B)(5.64 g, 22.0 mmol) was added. After stirring for a further 16 h at room temperature saturated aqueous sodium bicarbonate (60 cm3) was added and the organic material was extracted into ethyl acetate (60 cm3). The organic layer was then washed with a further portion of saturated aqueous sodium bicarbonate (40 cm3) before the aqueous fractions were combined and acidified to pH 5 with 5N hydrochloric acid. The desired material was then extracted from the acidified aqueous mixture into ethyl acetate (2×60 cm3), which was subsequently dried over sodium sulfate and evaporated under reduced pressure to afford the title compound (C) (6.1 g, 16.1 mmol, 73%).
