1.1: potassium tert-amyl oxide / benzene / 0.17 h / 0 - 20 °C 1.2: 90 percent / benzene / 0.5 h / 0 °C 2.1: 92 percent / lithium / tetrahydrofuran / 0.83 h / 15 - 20 °C / sonication 3.1: 100 percent / second generation Grubbs catalyst / benzene / 0.5 h / Heating 4.1: 77 percent / p-toluenesulfonic acid / benzene / 4 h / Heating View Scheme