A suspension of diethyl ether washed sodium hydride (1.22 g, 0.041 mole) in dry dimethylformamide (50 ml) under nitrogen at 0° C. was treated with a solution of 2-ethoxycarbonyl-6-(2,2,2-trichloroethoxycarbonyl)-4,5,6,7-tetrahydro-6-azaindole from Example 3 (13.4 g, 0.036 mole) in dry dimethylformamide (35 ml) dropwise over 10 minutes. Evolution of hydrogen was noted and the mixture stirred at room temperature for 10 minutes. The solution was cooled to 0° C. and treated dropwise with a solution of di-tert-butylcarbonate (8.94 g, 0.041 mole) in dry dimethylformamide (25 ml) over 10 minutes. The mixture was allowed to stand at room temperature overnight, water (100 ml) added and the resulting solution evaporated under vacuum to low bulk. The residue was diluted with water (200 ml) extracted with ethyl acetate (4×100 ml) the combined extracts washed with water (50 ml) and brine (3×100 ml), dried over sodium sulphate and evaporated to give a brown viscous oil, which was chromatographed on silica gel (250 g) eluting with hexane:dichloromethane (2:1), followed by dichloromethane to give the title product as a pure viscous oil (15.3 g, 80%). Found: C, 46.42; H, 5.08; N, 5.72. C18H23Cl3N2O6 requires C, 46.02; H, 4.93; N, 5.96%.
