Hydrochloric Acid → 3-Chloro-4-methyl-1,8-naphthyridine

Temperature

80 °C

N-(5-chloro-4-methyl-pyridin-2-yl)-2,2-dimethyl-propionamide (18.3 g, 0.081 mol) from Step 2 was placed in a flame-dried three-neck 1 L flask fitted with an overhead stirrer, under nitrogen. To this solid was added anhydrous diethyl ether (170 mL) and the mixture stirred until a solution, whereupon it was cooled in a dry ice/acetone bath for 20 min (slurry formed). To the resulting slurry was dropped in tert-butyl lithium (1.7 M in pentane, 100 mL) via cannula over an 8 min period. The flask was removed from the cooling bath and allowed to stir until it reached RT, at which time 3-dimethylamino-propenal (10 mL, 0.10 mol) was added neat. The resulting mixture was stirred overnight at RT under a nitrogen stream; by morning a dry powder resulted. To this was added water (80 mL) followed by slow addition of conc. HCl (40 mL) while cooling the flask in an ice/water bath. After the acid addition, the ice bath was removed and the flask was heated to 80° C. for 1 h, cooled in an ice/water bath and treated with NaOH (solid pellets) until basic. The basic aqueous mixture was subsequently extracted with DCM (4×100 mL)—patience and brine were required to help break the resulting emulsions. The combined extracts were dried over Na2SO4 and concentrated under vacuum to yield crude product, which was further purified by SGC (EtOAc eluant) to yield pure 3-chloro-4-methyl-[1,8]naphthyridine (10 g, 0.056 mol). Note: owing to weak UV activity, it was found more efficacious to monitor column fractions with MS rather than UV. MS (ESI+) for m/z 179 (M+H)+. 1H NMR (CDCl3) δ 9.06 (m, 1 H), 8.96 (s, 1 H), 8.34 (d, 1 H), 7.51 (m, 1H), 2.72 (s, 3H).

1. customfitted with an overhead stirrer, under nitrogen
2. temperaturewas cooled in a dry ice/acetone bath for 20 min
3. custom(slurry formed)
4. customThe flask was removed from the cooling bath
5. stirringto stir until it
6. additionwas added neat
7. stirringThe resulting mixture was stirred overnight at RT under a nitrogen stream
8. customby morning a dry powder resulted
9. temperaturewhile cooling the flask in an ice/water bath
10. additionAfter the acid addition
11. customthe ice bath was removed
12. temperaturecooled in an ice/water bath
13. additiontreated with NaOH (solid pellets) until basic
14. extractionThe basic aqueous mixture was subsequently extracted with DCM (4×100 mL)—patience and brine
15. dry with materialThe combined extracts were dried over Na2SO4
16. concentrationconcentrated under vacuum
17. customto yield crude product, which
18. customwas further purified by SGC (EtOAc eluant)

ORD record

ord-3e2fb42e796b49ce8ff836007b7f7380

Source dataset

uspto-grants-2008_12

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US07462600B2