Multi-step reaction with 12 steps 1: 915 mg / BF3*Et2O, 4 Angstroem molecular sieves / CH2Cl2 / 3 h / -40 °C2: 505 mg / 1percent NaOMe / methanol / 0.5 h / Ambient temperature3: 195 mg / (1R)-(-)-10-camphorsulfonic acid / dimethylformamide / 3 h / Ambient temperature4: 620 mg / BF3*Et2O, 4 Angstroem molecular sieves / CH2Cl2 / 4 h / -40 °C5: 218 mg / 1percent NaOMe / methanol / 0.5 h / Ambient temperature6: (1R)-(-)-10-camphorsulfonic acid / dimethylformamide / 2 h / Ambient temperature7: 210 mg / BF3*Et2O, 4 Angstroem molecular sieves / CH2Cl2 / 2 h / -40 °C8: 110 mg / 1percent NaOMe / methanol / 0.5 h / Ambient temperature9: 115 mg / (1R)-(-)-10-camphorsulfonic acid / dimethylformamide / 2 h / Ambient temperature10: 83 mg / BF3*Et2O, 4 Angstroem molecular sieves / CH2Cl2 / 2 h / -40 °C11: 33 mg / 1percent NaOMe / methanol / 0.33 h / Ambient temperature12: 24 mg / 1percent HCl / methanol / 2 h / Ambient temperature