1: 44 percent / imidazole / dimethylformamide / 12 h / Ambient temperature 2: 44 percent / tetrahydrofuran / 12 h / Ambient temperature 3: 61 percent / 40 percent HF / acetonitrile / 1 h / Ambient temperature 4: 32 percent / molecular sieve (4 Angstroem) / tetrahydrofuran / 14 h / Ambient temperature View Scheme