1: 72 percent / 1,5-diazabicyclo<4.3.0>non-5-ene (DBN) / tetrahydrofuran / 4.5 h / 0 - 20 °C 2: 100 percent / trifluoroacetic acid (TFA) / CDCl3 / 0.25 h / Ambient temperature; other solvents, var. pH, var. reaction times View Scheme

With  DBN in  tetrahydrofuran T=0 - 20°C; 4.5 h;   

With  3,5-dinitro benzoic acid in  dichloromethane 2 h;  Ambient temperature;