in toluene T=45 - 50°C; 1 h;

1: cis-maleic acid With 1-ethyl-(3-(3-dimethylamino)propyl)-carbodiimide hydrochloride in N,N-dimethyl-formamide T=20°C; 1 h; 2: cyclohexylamine in N,N-dimethyl-formamide T=20°C; 16 h;

acetic anhydride; triethylamine in acetone 20 h; Heating;

1: aq. HCl / methanol / 4 h / Heating 2: 55 percent / PPh3 / methanol / 3 h / Heating View Scheme