To a solution of 3-phenyl-1-(toluene-4-sulfonyl)-1H-indole-2-carbaldehyde (2.11 g, 5.62 mmol) in THF (30 mL) at −78° C. and under a nitrogen atmosphere, was added 3.0M methylmagnesium bromide in diethyl ether (2.6 mL). The mixture was stirred at 0° C. for 30 min then additional 3.0M methylmagnesium bromide in diethyl ether (0.3 mL) added. After 15 min, the reaction mixture was poured into a saturated solution of NH4Cl and extracted with EtOAc (×2). The combined organic fractions were washed with water, dried (Na2SO4) and concentrated in vacuo. The crude material was combined with a second portion of crude reaction mixture obtained following the same method (starting from 140 mg, 3.73 mmol of 3-phenyl-1-(toluene-4-sulfonyl)-1H-indole-2-carbaldehyde) and the combined batches were purified by column chromatography (Si—PCC, gradient 20-100% DCM in pentane) affording the title compound as a gum which solidified on standing (2.02 g, 86%). 1H NMR (CDCl3, 400 MHz): δ 8.07 (1H, d, J=8.35), 7.80-7.75 (2H, m), 7.51-7.38 (5H, m), 7.33-7.26 (2H, m), 7.20-7.14 (3H, m), 5.25-5.15 (1H, m), 4.06 (1H, d, J=11.01 Hz), 2.31 (3H, s), 1.70 (3H, d, J=6.88 Hz)
