1: propyl (S)-4-ethyl-3,4,7,8-tetrahydro-4-hydroxy-3,8-dioxo-1H-pyrano[3,4-c] pyridine-6-carboxylate With potassium carbonate in dimethyl sulfoxide T=50°C; 0.333333 h; 2: 2-Propenoic acid tert-butyl ester 20 h;

1: 74 percent / Cs2CO3 / dimethylsulfoxide / 21 h / 47 - 50 °C 2: 93.4 percent / trifluoroacetic acid; toluene / 2 h / 110 °C 3: p-TSA*H2O / toluene; acetic acid / 18 h / 95 - 100 °C View Scheme

1: 74 percent / Cs2CO3 / dimethylsulfoxide / 21 h / 47 - 50 °C 2: 93.4 percent / trifluoroacetic acid; toluene / 2 h / 110 °C 3: p-TSA*H2O / toluene; acetic acid / 18 h / 95 - 100 °C 4: pyridine / 2 h / 20 - 25 °C View Scheme

1: 74 percent / Cs2CO3 / dimethylsulfoxide / 21 h / 47 - 50 °C 2: 93.4 percent / trifluoroacetic acid; toluene / 2 h / 110 °C 3: p-TSA*H2O / toluene; acetic acid / 18 h / 95 - 100 °C View Scheme

1: 74 percent / Cs2CO3 / dimethylsulfoxide / 21 h / 47 - 50 °C 2: 93.4 percent / trifluoroacetic acid; toluene / 2 h / 110 °C View Scheme