Reaction Steps
A solution of t-butyl 4-formylbenzoate (8.52 g, 41 mmol) and methyl azidoacetate [M. S. Allen, L. K. Hamaker, A. J. La Loggia, J. M. Cook, Synth. Commun., 1992, 22, 2077-2102] (28.5 g, 248 mmol) in dry MeOH (200 mL) was added dropwise over 1 h to a solution of NaOMe (60 mL of a 3.3M solution in MeOH, 197 mmol) under nitrogen with cooling in an ice-salt bath. The yellow suspension was stirred for a further 1 h at 0° C., allowed to stand at 4° C. for 15 h, then diluted with water and the solid filtered off and dried in the dark. A solution of this crude azidocinnamate (8.76 g, 29 mmol) in dry xylene (400 mL) was added dropwise over 2 h to xylene (100 mL) at ref lux under nitrogen, the solution stirred at reflux for a further 1 h, then cooled and evaporated. Recrystallisation from MeOH gave t-butyl 2-(methoxycarbonyl)indole-6-carboxylate as a white solid (4.72 g, 42%), mp 189-190.5° C. 1H NMR [(CD3)2SO] δ12.26 (s, 1H, NH), 8.08 (s, 1H, H-3 or H-7), 7.73 (d, J=8.4 Hz, 1H, H-4), 7.61 (dd, J=8.4, 1.3 Hz, 1H, H-5), 7.21 (d, J=1.3 Hz, 1H, H-3 or H-7), 3.89 (s, 3H, CO2Me), 1.56 (s, 9H, CO2 tBu); 13C NMR δ165.5 (Co2 tBu), 161.4 (CO2Me), 136.5, 130.0, 129.9, 127.3 (C-2,6,8,9), 121.9, 120.3, 114.4, 107.5 (C-3,4,5,7), 80.4 (OCMe3), 52.1 (OCH3), 27.8 (tBu). Anal. (C15H17NO4) C,H,N.
