1: Et3N, SO3*pyridine / dimethylsulfoxide / 1 h / 20 °C 2: 1) potassium tert-butoxide / 1) THF, 10 deg C, 10 min, 2a) -78 up to -50 deg C, 1 h, 2b) -25 deg C, 30 min 3: methanol, HCl, acetyl chloride / 4 h / Heating View Scheme