BOP (6.59 g, 14.9 mmol) was added to a solution of 2,3-dihydrobenzo[b][1,4]dioxine-6-carboxylic acid (2.68 g, 14.9 mmol) and DIEA (5.3 mL, 30 mmol) in DMF (50 mL). Then (2R,4R)-1-tert-butyl 2-methyl 4-aminopiperidine-1,2-dicarboxylate (3.5 g, 13.5 mmol) was added to the mixture and the resulting solution was stirred at room temperature for 18 hours. Water (100 mL) was added to quench the reaction, and extracted with ethyl acetate (2×100 mL), organic layers were dried over MgSO4, and concentrated under reduced pressure. The residue was purified by Companion (ReadySep, 120 g, silica gel packed) with ethyl acetate/heptane from 20-50% to give the amide as off-white solid 5.4 g (95%). LC-MC: 421.2 (t=2.4 min).
