General procedure for the synthesis of 6-chloro-2H-benzopyran-3-carboxylic acid from 6-chloro-2H-benzopyran-3-carbonitrile:
1. 5-Chloro-2-hydroxybenzaldehyde (compound 15a, 10.0 mmol, 1.7 g), acrylonitrile (50.0 mmol, 2.14 mL) and DABCO (2.33 mmol, 0.26 g) were mixed and heated to reflux overnight using an oil bath. After the reaction was completed, the flask was cooled to room temperature, ether (Et2O, 100 mL) was added, and the ether layer was washed sequentially with 10% NaOH solution and 1N HCl brine. The organic layer was dried with MgSO4, filtered and the solvent was removed in vacuum to afford 6-chloro-2H-benzopyran-3-carbonitrile (Compound 15b, yellow solid, 1.42 g, 74% yield), which could be used in the next reaction without further purification.
2. In a round-bottomed flask containing compound 15b (7.43 mmol, 1.42 g), THF (2 mL) and 10% NaOH solution (100 mL) were added and the solution was heated to reflux for 4 hours. After completion of the reaction, the flask was immersed in an ice bath and slowly acidified by addition of hydrochloric acid. The resulting pale yellow solid was filtered and dried under vacuum to give 6-chloro-2H-benzopyran-3-carboxylic acid (compound 15c, 1.02 g, 65% yield).
3. Sodium triacetoxyborohydride (3.5 mmol, 0.75 g) was added to the mixture of 4-nitrofluorobenzene (compound 15d) and stirred for 12 h at room temperature. The reaction progress was monitored by mass spectrometry (MS m/e 247, 100%). Subsequently, aqueous formaldehyde (37%, 9.6 mmol, 0.8 mL) and sodium triacetoxyborohydride (3.5 mmol, 0.75 g) were added to the reaction mixture and stirring was continued for 2 h at room temperature. The reaction mixture was alkalized with 2N NaOH solution and extracted with CH2Cl2. The organic layer was washed sequentially with water and brine and dried over Na2SO4. The solvent was removed in vacuum after filtration to afford (2S)-dicyclo[2.2.1]hept-2-ylmethyl-(4-nitrobenzyl)amine (Compound 15e, yellow oil, 0.72 g, 98% yield, MS m/e 261 [M+H, 100%]), which can be used in the next step of the reaction without further purification.
4. SnCl2-2H2O (10.4 mmol, 2.35 g) was added to a solution of compound 15e (2.76 mmol, 0.72 g) in EtOH (25 mL) at room temperature and stirred for 2 days. The solvent was removed in vacuum and the residue was alkalized with 2N NaOH solution and the aqueous layer was extracted with CH2Cl2 (2 x 30 mL). The combined organic layers were dried with Na2SO4, filtered and the solvent was removed in vacuum to afford (2S)-(4-aminobenzyl)-dicyclo[2.2.1]hept-2-ylmethylamine (Compound 15f, yellow oil, 0.54 g, 85% yield, MS m/e 231 [M+H, 100%]), which was used in the next reaction without further purification.
5. EDCI (0.33 mmol, 0.07 g) was added in a single addition to DMF (5.0 mL) of compound 15f (0.24 mmol, 0.06 g), 6-chloro-2H-benzopyran-3-carboxylic acid (compound 15g, 0.22 mmol, 0.04 g), and HOAt (0.22 mmol, 0.03 g) at 0 °C in the suspension. After heating the suspension to room temperature, DMAP and Et3N (0.65 mmol, 0.1 mL) were added and stirred overnight. After the reaction was completed, the orange-yellow suspension was poured into water and extracted with EtOAc (25 mL). The organic layer was washed sequentially with water (2 × 20 mL), 5% NaOH solution (10 mL) and brine, dried over Na2SO4 and filtered, and the solvent was removed in vacuum. The residue was purified by preparative TLC (15:1 CH2Cl2/MeOH) to afford 6-chloro-2H-benzopyran-3-carboxylic acid (2S)-{4-[(dicyclo[2.2.1]hept-2-ylmethylamino)methyl]phenyl} amide (Compound 15h, light yellow solid, 0.06 g, 61% yield, MS m/e 423 [M+H, 100%] ).
6. iodomethane (0.5 mL) was added to a solution of CH2Cl2 (1.0 mL) of compound 15h (0.08 mmol, 0.03 g) at room temperature and allowed to stand overnight. After a yellow precipitate was observed, the solvent was removed under vacuum. The residue was washed with Et2O to afford compound 15i (yellow solid, 0.05 g, 96% yield, MS m/e 437 [M+H, 100%]).
