[NH:1]1[CH2:11][CH2:10][CH:4]([C:5]([O:7][CH2:8][CH3:9])=[O:6])[CH2:3][CH2:2]1.C(N(CC)CC)C.[CH3:19][C:20]([CH3:25])([CH3:24])[C:21](Cl)=[O:22]>ClCCl>[C:21]([N:1]1[CH2:2][CH2:3][CH:4]([C:5]([O:7][CH2:8][CH3:9])=[O:6])[CH2:10][CH2:11]1)(=[O:22])[C:20]([CH3:25])([CH3:24])[CH3:19]Ethyl isonipecotate (20 mL, 130 mmol) was dissolved in 130 mL of dichloromethane and cooled to 0° C. and triethyl amine (19.9 mL, 143 mmol) was added. Trimethylacetyl chloride (16.8 mL, 136 mmol) was added dropwise and the reaction was allowed to warm to rt and stirred for 16 h. The reaction mixture was washed with hydrochloric acid solution (1.0 M, aq), sodium bicarbonate (sat., aq.) and sodium chloride (sat., aq.). The organic layer dried over magnesium sulfate, filtered and the solvent removed to provide 29.5 g (94%) of 20a as a pale orange liquid. LC-MS m/z 242 [M+H]+.
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