methanesulfonic acid in dichloromethane T=20°C; 1 h;

1: hex-1-en-5-yne With lithium hexamethyldisilazane in tetrahydrofuran T=-78°C; 2: With tBuOOLi in tetrahydrofuran; toluene T=-78 - 0°C; 2.5 h; 3: tri-isopropylsylil trifluoromethane sulfonate in tetrahydrofuran; toluene T=0°C; 0.5 h;