HCID 86584125, compound → HCID 69984158, compound

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 dichloromethane (250 mL) at room temperature. After 2 hr, this was filtered and the solid was washed with additional anhydrous dichloromethane. The solvent was removed from the filtrate and the crystalline residue was dissolved in anhydrous dichloromethane (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 room temperature. 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% dichloromethane 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=11.9 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 N,N-dimethylformamide (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 dichloromethane (24 mL) was stirred at room temperature for 3 hr. The reaction mixture was diluted with dichloromethane, 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).

1. extractionThe reaction was then extracted with EtOAc (twice) and the combined organic extracts
2. washwere washed with sat. aqueous NaHCO3 solution (twice), 20% aqueous NaHSO3 solution, sat. aqueous NaHCO3 solution and brine
3. dry with materialAfter being dried (Na2SO4)
4. customthe solvents were removed
5. customthe residue was chromatographed on a silica gel column (gradient elution with portions of hexane containing 10 to 40% EtOAc)

ORD record

ord-06d065d547214a859074df1391e26a6f

Source dataset

uspto-grants-2003_03

DOI

10.6084/m9.figshare.5104873.v1

Patent number

US06537988B2