1: 67 percent / n-butyl lithium, tetramethylethylenediamine / tetrahydrofuran 2: 88 percent / boron trichloride 3: 27 percent / Zn/Hg, 6N HCl / toluene / 2 h / Heating 4: 66 percent / oxygen, salcomine / dimethylformamide View Scheme