1: With tert.-butyl lithium in diethyl ether; pentane T=-70 - -50°C; 0.2 h; 2: With sulfur dioxide in diethyl ether; pentane T=-50 - 0°C; 3: With N-chloro-succinimide in diethyl ether; pentane T=0 - 20°C; 0.75 h;