Trifluoroacetic acid → 1-(2,2-Dimethylpropyl)-5-(1,2,3,3a,4,6a-hexahydrocyclopenta[c]pyrrol-5-yl)-3-methyl-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one

tert-Butyl 5-[1-(2,2-dimethylpropyl)-3-methyl-2-oxo-2,3-dihydro-1H-imidazo-[4,5-b]pyridin-5-yl]-3,3a,4,6a-tetrahydrocyclopenta[c]pyrrole-2(1H)-carboxylate (8-3, 1 g, 2.3 mmol) was added to a mixture of dichloromethane (18.7 mL) and trifluoroacetic acid (4.6 mL) at room temperature. After stirring for 18 h, the solvent was removed in vacuo. The resulting residue was then diluted with ethyl acetate (100 mL) and washed sequentially with saturated sodium bicarbonate (2×50 mL), water (1×50 mL) and brine (1×50 mL). The organics were dried over magnesium sulfate, filtered, and concentrated in vacuo to give 1-(2,2-Dimethylpropyl)-5-(1,2,3,3a,4,6a-hexahydrocyclopenta[c]pyrrol-5-yl)-3-methyl-1,3-dihydro-2H-imidazo[4,5-b]pyridin-2-one (8-4) as a white solid. This material was carried on without further purification.