General procedure for the synthesis of 1-Boc-azetidine-3-carboxylic acid from di-tert-butyl dicarbonate and 3-acridinecarboxylic acid:
Example 4 Synthesis of 6-(3-{[(benzylsulfonyl)amino]carbonyl}azetidin-1-yl)-5-cyano-2-(difluoromethyl)nicotinate
(a) Preparation of ethyl 1-(tert-butoxycarbonyl)azetidine-3-carboxylate
Di-tert-butyl dicarbonate (25.535 g, 117 mmol) dissolved in methanol (70 mL) was added dropwise to a stirred solution of azetidine-3-carboxylic acid (10.11 g, 100 mmol) and triethylamine (27.8 mL, 200 mmol) in methanol (105 mL) over a period of 20 min. The reaction was carried out at room temperature (mild exotherm was observed) with continuous stirring for 18 hours. Upon completion of the reaction, the mixture was evaporated to dryness, tetrahydrofuran (120 mL) was added and evaporated again to afford the crude 1-(tert-butoxycarbonyl)azetidine-3-carboxylic acid, which could be used in the next step without further purification.
Yield: 25.89 g (128%).
1H NMR (400 MHz, CDCl3) δ 1.43 (9H, s), 3.21-3.34 (1H, m), 4.00-4.13 (4H, m).
