indole (Aldrich)
diethyl ether (Fisher)
oxalyl chloride (Aldrich)
tris(2-aminoethyl)amine (Aldrich)
triethylamine (Aldrich)
THF (Aldrich)
methanol (Fisher)

To indole (10.07 g, 86.1 mmol) in ether (200 mL) was added dropwise oxalyl choride (14.6 g, 114.6 mmol) over 15 mins. After stirring for 30 min, the solution was filtered to yield indole-3-glyoxalyl chloride as a yellow solid, which was rapidly dissolved in THF (50 mL). To the indole-3-glyoxalyl chloride in THF at 0°C was added a solution of tris(2-aminoethyl)amine (6.14 g, 42.0 mmol) and triethylamine (42.3 mmol) in THF (10 mL). After stirring at 0°C for 1 h, the solution was filtered and the filtrate was evaporated to yield tris(2-[indole-3-glyoxylamido]ethyl)amine as a beige solid, which was recrystallized in MeOH to yield glassy crystals.

The reaction is an efficient way to prepare tris(2-[indole-3-glyoxylamido]ethyl)amine. The glyoxalyl choride intermediate is unstable, thus cold temperatures are necessary. Could be reliable with other acyl chlorides.

Yield 5.93 g (31.4%); mp > 250°C. ¹H NMR (250 MHz, DMSO-d₆) _8.75 (s, 3H), 8.65 (t, J=5.29 Hz, 3H), 8.14 (d, J=6.9 Hz, 3H), 7.47 (d, J=7.1 Hz, 3H), 7.22 (t, J=7.0 Hz, 3H), 7.16 (t, J=7.0 Hz, 3H), 3.31 (m, 6H, Ha), 2.71 (bt, 6H, Hb); MS (M+1)⁺ = 660 for C₃₆H₃₃N₇O₆

Carpenter, R. A.; Farley, A. R.; Cox, J. R.; Dobson, A. J.; Whitlock, C. R. J. Undergrad. Chem. Res. 2004, 1, 114.