tert.-butyl lithium in diethyl ether; pentane inert atmosphere; dropwise addn. of tBuLi soln. (pentane, -78°C,15 min) to alcohol soln. (Et2O), stirring (-78°C, 30 min, -40°C, 2.5 h), Bu3SnCl addn. (6 min), stirring (1.5 h), quenching (pH 7buffer / H2O, -40°C); extg. (Et2O, room temp.), drying (Na2SO4), concg., chromy. (EtOAc / hexanes = 1 : 15 + 1 percent Et3N);

potassium hydroxide