To a chilled (0° C.), stirred solution of 1,2,3,3a,8,8a-hexahydro-α-oxo-1,3a,8-trimethyl-5-pyrrolo[2,3-b]indole acetic acid, ethyl ester (0.68 g) in anhydrous isopropyl alcohol (10.2 ml) was added titanium (IV) ethoxide (0.17 ml) via syringe under a nitrogen atmosphere. The solution was warmed to room temperature and refluxed for 6.5 hours. The isopropyl alcohol was removed under reduced pressure and the residue dissolved in ethyl acetate (100 ml). The solution was washed twice with 50 ml portions of saturated aqueous NH4Cl solution, twice with 50 ml portions of saturated aqueous NaHCO3 solution and once with 50 ml of brine. The organic and aqueous phases were separated and the organic phase dried (Na2SO4), filtered, and concentrated to an oil. The crude mixture was purified using preparative HPLC (silica gel, 35% ethyl acetate in dichloromethane as the loading solvent and eluent). The appropriate fractions were combined and the solvents were removed under reduced pressure yielding 0.54 g of 1,2,3,3 a,8,8a-hexahydro-α-oxo-1,3a,8-trimethyl-5-pyrrolo[2,3-b]indole acetic acid, isopropyl ester, as an oil.
