diethyl-1,4-dihydro-2,6-dimethyl-3,5-pyridine dicarboxylate; L-proline in dichloromethane T=25°C; 3 h;

methanol; triethylamine 1.) benzene, reflux, 20 h, 2.) room temperature, 12 h;

1: 87 percent / tetrahydrofuran / 17 h / Ambient temperature 2: 43 percent / 1.) triethylamine, 2.) aq. methanol / 1.) benzene, reflux, 20 h, 2.) room temperature, 12 h View Scheme

1: 88 percent / 1.) LDA / tetrahydrofuran; hexane / 1.) -70 deg C, 0.5 h, 2.) room temperature, 0.5 h 2: 87 percent / tetrahydrofuran / 17 h / Ambient temperature 3: 43 percent / 1.) triethylamine, 2.) aq. methanol / 1.) benzene, reflux, 20 h, 2.) room temperature, 12 h View Scheme

1: bromine / chloroform / 0 - 20 °C 2: 2 h / 130 °C / neat (no solvent) View Scheme