1: With N-(chloromethylene)-N-methylmethanaminium chloride in pyridine T=20°C; 2 h; 2: With N-ethyl-N,N-diisopropylamine in tetrahydrofuran T=20°C; 3 h; 3: With 1,8-diazabicyclo[5.4.0]undec-7-ene in tetrahydrofuran Heating; Further stages.;