APPLICATION
TCI Practical Example: Preparation of Weinreb Amide Using N,O-dimethylhydroxylamine Hydrochloride
Used Chemicals
N,O-Dimethylhydroxylamine Hydrochloride [D1899]
Acryloyl Chloride
Sodium Hydrogen Carbonate [S0561]
Dichloromethane
Procedure
N,O-Dimethylhydroxylamine hydrochloride (646.7 mg, 6.63 mmol, 1.2 eq.) was added to a solution of acryloyl chloride (0.45 mL, 500 mg, 5.52 mmol) and NaHCO3 (1.16 g, 13.8 mmol, 2.5 eq.) in dry dichloromethane (4.6 mL) at 0 °C. The mixture was stirred for overnight at room temperature. The reaction mixture was quenched with 3 mol/L HCl (10 mL) and the two layers were separated. The organic layer was washed with sat. NaHCO3 aq. (10 mL) and brine, dried over sodium sulfate, filtered, and concentrated under reduced pressure to give the Weinreb amide 1 as a colorless liquid (413 mg, 65% yield).
Experimenter’s Comments
The reaction mixture was monitored by TLC (ethyl acetate:hexane = 1:1, Rf = 0.55).
Analytical Data
Weinreb amide 1
1H NMR (270 MHz, CDCl3); δ 6.74 (dd, J = 10.1, 17.1 Hz, 1H), 6.43 (dd, J = 2.3, 17.1 Hz, 1H), 5.76 (dd, J = 2.3, 10.1 Hz, 1H), 3.71 (s, 3H), 3.27 (s, 3H).
Other Reference
Concise stereoselective and stereodivergent syntheses of (±)-melicolones A and B
Z. Wang, S. F. Martin, Tetrahedron 2022, 103, 132551.
Application
Weinreb Ketone Synthesis
Typical procedure (Preparation of Weinreb’s amides from acid chlorides): Acid chloride (1 mmol) and N,O-dimethylhydroxylamine hydrochloride (110mg, 1.1 mmol) are dissolved in ethanol-free chloroform (10 mL) at room temperature. The solution is cooled to 0 °C and pyridine (185 mg, 2.2 mmol) is added. The mixture is stirred at rt for 1 h and evaporated in vacuo. The residue is dissolved in a 1:1 mixture of diethylether and methylene chloride, and washed with brine. The organic layer is dried over anhydrous sodium sulfate and concentrated to give the Weinreb’s amide which is purified by silica gel chromatography or by distillation.
PRECAUTIONARY STATEMENTS
P264 : Wash skin thoroughly after handling.
P280 : Wear protective gloves/ eye protection/ face protection.
P337 + P313 : If eye irritation persists: Get medical advice/ attention.
P305 + P351 + P338 : IF IN EYES: Rinse cautiously with water for several minutes. Remove contact lenses, if present and easy to do. Continue rinsing.
P302 + P352 : IF ON SKIN: Wash with plenty of soap and water.
P332 + P313 : If skin irritation occurs: Get medical advice/ attention.
P362 : Take off contaminated clothing and wash before reuse.
QUALITY CERTIFICATION / COMPLIANCE
Fukaya factory is certified for GMP, ISO14001:2004 (JQA-EM5386) and IQ Net (JP-JQA-EM5386).
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