1: MeLi / tetrahydrofuran / 0.25 h / -78 °C 2: 1)n-Bu3P / 1) CuBr*Me2S, 2.) BF3*Et2O / 1)THF, -78 deg C, 20 min 2)-78 deg C, 1 h, then -40 deg C, 2 h View Scheme

copper(I) bromide dimethylsulfide complex; boron trifluoride diethyl etherate in tetrahydrofuran T=-78°C; 3 h;

tributylphosphine; copper(I) bromide dimethylsulfide complex; boron trifluoride diethyl etherate 1)THF, -78 deg C, 20 min 2)-78 deg C, 1 h, then -40 deg C, 2 h; Yield given. Multistep reaction;

Yield given. Multistep reaction;