[CH3:1][O:2][C:3]1[C:9]([CH3:10])=[CH:8][C:6]([NH2:7])=[C:5]([CH3:11])[C:4]=1[CH3:12].[CH:13]([C:15]1([C:19]([O:21][CH2:22][CH3:23])=[O:20])[CH2:18][CH2:17][CH2:16]1)=O.[BH-](OC(C)=O)(OC(C)=O)OC(C)=O.[Na+].C(O)(=O)C>ClCCl.O>[CH3:1][O:2][C:3]1[C:9]([CH3:10])=[CH:8][C:6]([NH:7][CH2:13][C:15]2([C:19]([O:21][CH2:22][CH3:23])=[O:20])[CH2:18][CH2:17][CH2:16]2)=[C:5]([CH3:11])[C:4]=1[CH3:12]To a solution of 4-methoxy-2,3,5-trimethylaniline (400 mg) in dichloromethane (24 mL) was added ethyl 1-formylcyclobutanecarboxylate, prepared as described in Step 1 (377.8 μL). Then NaBH(OAc)3 (771.4 mg) and acetic acid (152.2 μL) were added sequentially. After 3.5 h, water was added. The two layers were separated and the aqueous layer was extracted with more dichloromethane. The combined organic phases were washed with brine, dried and evaporated. Elution of the residue on a silica column (EtOAc/DCM, 0-5%) gave ethyl 1-((4-methoxy-2,3,5-trimethylphenylamino)methyl)-cyclobutanecarboxylate (400 mg) as an oil. 1H-NMR, (300 MHz, CDCl3) δ=6.37 (s,1H), 4.262-3.974 (q, 2H), 3.63 (s, 3H), 3.745-3.474 (br s, 1H), 3.41 (s, 2H), 2.693-2.339 (m, 2H), 2.27 (s, 3H), 2.21, (s, 3H), 2.14-1.818, (m, 4H), 2.02, (s, 3H), 1.333-1.174 (t, 3H) ppm., 13C-NMR, (75 MHz, CDCl3) δ=176.51, 142.52, 129.68, 128.09, 119.78, 110.29, 60.85, 60.37, 50.67, 47.2, 28.43, 16.38, 15.9, 14.3, 12.94, 12.85 ppm.
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