1.1: urea / 0.5 h / 220 °C 2.1: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux 3.1: nitric acid / acetic acid / 4 h / 0 °C 4.1: sodium dithionite / water / 3 h / 50 °C 4.2: 0.5 h / 65 °C View Scheme

1: urea / 0.5 h / 220 °C 2: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux 3: nitric acid / acetic acid / 4 h / 0 °C View Scheme

1.1: urea / 0.5 h / 220 °C 2.1: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux 3.1: nitric acid / acetic acid / 4 h / 0 °C 4.1: sodium dithionite / water / 3 h / 50 °C 4.2: 0.5 h / 65 °C 5.1: acetic acid; N,N-dimethyl-formamide dimethyl acetal / toluene / 4 h / 105 °C 6.1: acetic acid / toluene / 5 h / 60 °C 7.1: toluene / 5 h / 125 °C View Scheme

1.1: urea / 0.5 h / 220 °C 2.1: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux 3.1: nitric acid / acetic acid / 4 h / 0 °C 4.1: sodium dithionite / water / 3 h / 50 °C 4.2: 0.5 h / 65 °C 5.1: acetic acid; N,N-dimethyl-formamide dimethyl acetal / toluene / 4 h / 105 °C 6.1: acetic acid / toluene / 5 h / 60 °C 7.1: toluene / 5 h / 125 °C 8.1: hydrogenchloride / methanol / 0.05 h / 15 - 20 °C View Scheme

1: urea / 0.5 h / 220 °C 2: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux View Scheme

1.1: urea / 0.5 h / 220 °C 2.1: phosphorous pentoxide / anhydrous xylene / 18 h / Reflux 3.1: nitric acid / acetic acid / 4 h / 0 °C 4.1: sodium dithionite / water / 3 h / 50 °C 4.2: 0.5 h / 65 °C 5.1: acetic acid; N,N-dimethyl-formamide dimethyl acetal / toluene / 4 h / 105 °C View Scheme