Urea Formation

(Curtius Rearrangement)

Examples:

Example 1

To a solution of A (14.6 g, 110.6 mmol) in toluene (530 mL) was added DPPA (30.4 g, 110.5 mmol), followed by TEA (18.3 g, 181.2 mmol). The mixture was stirred at RT for 30 min, then B (15.9 g, 73.61 mmol) was added. The reaction mixture was stirred at reflux for 6 h. The mixture was diluted with EtOAc (530 mL) and washed with brine (2 x 300 mL). The combined aq layers were acidified to pH 5 using 2N HCl, causing solids to form. The resulting solids were filtered and dried to provide the product as a pale yellow solid. [15 g, 39.3%]

[Patent Reference: WO2016023830, page 60, (5.1 MB)]