1: With sec.-butyllithium in tetrahydrofuran; hexane; cyclohexane T=-78°C; 0.5 h; Inert atmosphere; 2: With N-fluoro-N-(phenylsulfonyl)benzene-sulfonamide in tetrahydrofuran; hexane; cyclohexane T=-78 - 20°C; Inert atmosphere; 3: With tetrabutyl ammonium fluoride in tetrahydrofuran T=20°C; 3 h; Overall yield = 460 mg;