1-Cyclobutyl-6-ethoxy-2-(4-ethylaminophenyl)-1H-indole-3-carbonitrile (35 mg, 0.10 mmol), prepared as in example 1CO, step C, is dissolved in pyridine (300 μL). Cyclopentyl chloroformate (25 μL, 0.17 mmol) is added. The reaction mixture is stirred at room temperature for 2.5 h. More chloroformate (10 μL, 0.07 mmol) is added to drive the reaction to completion. After an additional 90 min of stirring, the reaction mixture is partitioned between aqueous HCl and EtOAc. The organic layer is dried and concentrated. Purification by silica gel chromatography yields [4-(3-cyano-1-cyclobutyl-6-ethoxy-1H-indol-2-yl)-phenyl]-ethyl-carbamic acid cyclopentyl ester (41 mg, 87%) as a white solid.
