4-Methylbenzene-1,2-diamine (1.65 g, 13.5 mmol) was added to a mixture of (2R,4R)-1-(tert-butoxycarbonyl)-4-(2,3-dihydrobenzo[b][1,4]dioxine-6-carboxamido)piperidine-2-carboxylic acid (5.0 g, 12 mmol), BOP (5.71 g, 12.9 mmol) and DIEA (4.3 mL, 24.6 mmol) in DMF (30 mL), and the resulting solution was stirred at room temperature for 8 hours. Water (100 mL) was added to the reaction mixture and then extracted with ethyl acetate (2×100 mL). The organic layers were dried over MgSO4 and concentrated to give a red solid. Purification was done by Companion (ReadySep, 120 g, silica gel packed) with methanol/methylenechloride from 1-5% to give the title compound as a brown solid 4.85 g (80%). LC-MS: 511.2 (t=2.4 min).
