triethylamine in dichloromethane 2 h; Ambient temperature;

1: 1) tert-butyllithium / 1) THF, -78 deg C, 1.5 h; 2) THF, -78 deg C, 30 min 2: 65 percent / tetrahydrofuran / 0.5 h / -78 °C 3: 93 percent / 3N-aq. HCl / dioxane; H2O / 4 h / Heating View Scheme