Multi-step reaction with 6 steps 1: DMAP / diethyl ether / 4 h / 20 °C2: 2.19 g / sodium borohydride / ethanol / 2 h / 20 °C3: 66 percent / potassium tert-butoxide / 2-methyl-propan-2-ol; tetrahydrofuran / 21 h / 20 °C4: DMAP / diethyl ether / 2 h / 20 °C5: 0.14 g / DMAP / CH2Cl2 / 3 h / 20 °C6: 53 percent / aq. HCl / 12 h / Heating