Reaktion #440452

Reaktionsgleichung

Triethylamine

Trimethylacetaldehyde

p-anisidine

Na2SO4

Benzyloxyacetyl chloride

→

(±)-cis-4-tert-butyl-3-benzyloxy-1-p-methoxybenzyl-azetidinone

Ausbeute 92.0%

Lösungsmittel

DCM

Reaktionsbedingungen

Aufarbeitung

1. 1
   Filtrationthis was filtered
2. 2
   Waschenthe solid was washed with additional anhydrous DCM
3. 3
   SonstigeThe solvent was removed from the filtrate
4. 4
   workup.DISSOLUTIONthe crystalline residue was dissolved in anhydrous DCM (750 mL)
5. 5
   Temperaturto warm to RT
6. 6
   workup.WAITAfter 24 hr
7. 7
   Waschenthis was washed with 0.5 M HCl (twice), sat. aqueous NaHCO3 solution, brine
8. 8
   Trocknendried (Na2SO4)
9. 9
   SonstigeThe solvent was removed
10. 10
    Sonstigethe residue was chromatographed on a silica gel column (gradient elution with 20% DCM in hexane containing 0 to 20% EtOAc)

Vorschrift

Trimethylacetaldehyde (20.3 mL, 1.25 equiv) was added to a strirred suspension of p-anisidine (18.4 gm, 0.150 mole) and anhydrous Na2SO4 (150 gm) in anhydrous DCM (250 mL) at RT. After 2 hr, this was filtered and the solid was washed with additional anhydrous DCM. The solvent was removed from the filtrate and the crystalline residue was dissolved in anhydrous DCM (750 mL) and placed under a nitrogen atmosphere. Triethylamine (48.0 mL, 2.3 equiv) was added and the reaction was cooled to −78° C. Benzyloxyacetyl chloride (27.2 mL 1.15 equiv) was added dropwise and then the reaction was allowed to warm to RT. After 24 hr, this was washed with 0.5 M HCl (twice), sat. aqueous NaHCO3 solution, brine and dried (Na2SO4). The solvent was removed and the residue was chromatographed on a silica gel column (gradient elution with 20% DCM in hexane containing 0 to 20% EtOAc) to afford (±)-cis-4-tert-butyl-3-benzyloxy-1-p-methoxybenzyl-azetidinone as a crystalline solid (46.9 gm, 92%): 1H NMR (CDCl3) δ 1.09 (s, 9H), 3.81 (s, 3H), 4.15 (d, 1H, J=5.5 Hz), 4.77 (d, 1H, J=11.9 Hz), 4.81 (d, 1H, J=5.5 Hz), 5.03 (d, 1H, J=1.9 Hz) 6.87-7.43 (m, 9 Hz); LRMS (ESI) 340 ([M+H]+). A solution of ceric ammonium nitrate (60.4 gm 3.6 equiv) in 900 mL of water was added to a well stirred solution of the azetidinone (10.38 gm, 30.6 mmole) in acetonitrile (600 mL) in an ice bath over 1 hr. The reaction was then extracted with EtOAc (twice) and the combined organic extracts were washed with sat. aqueous NaHCO3 solution (twice), 20% aqueous NaHSO3 solution, sat. aqueous NaHCO3 solution and brine. After being dried (Na2SO4), the solvents were removed and the residue was chromatographed on a silica gel column (gradient elution with portions of hexane containing 10 to 40% EtOAc) to afford 5.64 gm of slightly impure (±)-cis-3-benzyloxy-4-tert-butyl-azetidin-2-one: 1H NMR (CDCl3) δ 1.04 (s, 9H), 3.51 (d, 1H, J=5.2 Hz), 4.71 (m, 2H), 4.96 (d, 1H, J=11.9 Hz) 6.10 (brs, 1H), 7.35 (m, 5H). A suspension of this material (5.54 gm, 23.8 mmole) and 2.5 gm of 10% Pd on charcoal in absolute EtOH (100 mL) was hydrogenated (34 psi H2, Parr apparatus) for 23 hr. A further 2 gm of the Pd catalyst was added and the hydrogenation was continued for a further 17 hr at 50 psi H2. The catalyst was removed by filtration and the solvent was removed from the filtrate to leave crude (±)-cis-3-hydroxy-4-(tert-butyl)-azetidin-2-one: 1H NMR (CDCl3+1 drop D2O) δ 1.05 (s, 9H), 3.48 (d, 1H, J=5.0 Hz), 4.98 (d, 1H, J=5.0 Hz). This material was dissolved in dry DMF (40 mL) and imidazole (3.24 gm, 2 equiv) and triethylsilyl chloride (4.0 mL, 1 equiv) were added. After 10 min, the reaction was partitioned between water and a mixture of EtOAc and hexane (1:1). The organic phase was washed with water (twice), brine and then dried (Na2SO4). The solvents were removed and the residue was chromatographed on a silica gel column (gradient elution with 20 to 25% EtOAc in hexane) to give (±)-cis-4-tert-butyl-3-triethylsilyloxy-azetidin-2-one (3.86 gm): 1H NMR (CDCl3) δ 0.70 (m, 6H), 0.98 (m, 18H), 3.39 (d, 1H, J=5.0 Hz), 4.88 (dd, 1H, J=2.1, 5.0 Hz), 6.08 (brs, 1H). A solution of this azetidinone (2.04 gm, 7.92 mmole), diisopropylethyl amine (1.66 mL, 1.2 equiv), di-tert-butyl dicarbonate (1.90 gm, 1.1 equiv) and p-dimethylaminopyridine (194 mg, 0.2 equiv) in dry DCM (24 mL) was left stirring at RT for 3 hr. The reaction was diluted with DCM, washed with brine and dried (Na2SO4). Removal of the solvent followed by silica gel column chromatography (gradient elution with 0 to 20% EtOAc in hexane) afforded 2.71 gm (96%) of the title compound as an oil: 1H NMR (CDCl3) δ 0.70 (m, 6H), 1.00 (m, 9H), 1.09 (s, 9H), 1.53 (s, 9H), 3.90 (d, 1H, J=6.5 Hz), 4.93 (d, 1H, J=6.5 Hz).

Quelle