A solution of 4-ethyl-3-methoxy-benzoic acid (450 mg, 2.5 mmol), HATU (940 mg, 2.5 mmol), methyl spiro[piperidine-4,4′-pyrrolo[2,1-c][1,4]benzoxazine]-7′-carboxylate (830 mg, 2.5 mmol), and Et3N (1.7 mL, 9.9 mmol) in DMF (8 mL) was stirred at room temperature overnight. The reaction was diluted with ethyl acetate and washed with saturated sodium bicarbonate solution. The organics were dried over sodium sulfate, filtered and evaporated to yield a crude mixture that was purified by silica gel chromatography eluting with 0-30% EtOAc in hexanes to yield methyl 1′-(4-ethyl-3-methoxybenzoyl)spiro[benzo[b]pyrrolo[1,2-d][1,4]oxazine-4,4′-piperidine]-7-carboxylate (1.1 g, quant). ESI-MS m/z calc. 460.5, found 461.5 (M+1)+; Retention time: 2.08 minutes (3 min run).
