Methyl 3-(4-benzyloxyphenyl)-4-ethylpyrrolo[2,1,5-cd]indolizine-1-carboxylate (2.92 g, 7.13 mmol) was dissolved in 200 ml of methanol and 20 ml of water. Potassium hydroxide (6.40 g, 114 mmol) was added and the mixture was heated to reflux for 3 days. The reaction mixture was allowed to cool to room temperature and the methanol was evaporated. The orange solid was partitioned between 200 ml of dichloromethane and 200 ml of 1M hydrochloric acid and acidified with concentrated hydrochloric acid until pH=1. This resulted in the formation of a suspension. A further 800 ml of dichloromethane and 200 ml of water was added and the suspension was filtered to give 0.74 g (26%) of 3-(4-benzyloxyphenyl)-4-ethylpyrrolo[2,1,5-cd]indolizine-1-carboxylic acid as a yellow solid. The organic solution was washed with brine, dried over magnesium sulfate and evaporated to give a orange solid. This solid was recrystallised from acetone to afford 1.23 g (43%) of 3-(4-benzyloxyphenyl)-4-ethylpyrrolo[2,1,5-cd]indolizine-1-carboxylic acid as a yellow solid. M.p. 223-224° C. MS(SP): m/z 395 (M+). 1H-NMR (DMSO-d6, 200 MHz) δ: 1.41 (t, 3H); 3.02 (q, 2H); 5.22 (s, 2H); 7.24 (d, 2H); 7.31-7.56 (m, 5H); 7.81 (d, 2H); 7.95 (t, 1H); 8.03 (s, 1H); 8.20 (d, 1H); 8.32 (d, 1H); 12.46 (bs, 1H).
