In a 5 mL reaction tube was added acetic acid (5 ml) followed by (E)-tert-butyl 1-(4-(3-(dimethylamino)-2-phenylacryloyl)phenyl)cyclobutylcarbamate (750 mg, 1.783 mmol), 2H-pyran-3,5(4H,6H)-dione (305 mg, 2.68 mmol), ammonium acetate (412 mg, 5.35 mmol) and molecular sieves (100 mg) to give a brown suspension. The reaction mixture was stirred at 100° C. under a nitrogen atmosphere for 2 hours, then allowed to cool to room temperature and concentrated under reduced pressure. The residue was partitioned between water (10 mL) and dichloromethane (10 mL) and decanted from the molecular sieves. The layers were separated and the aqueous phase extracted into dichloromethane (2×10 mL). The combined organic phases were washed with saturated sodium bicarbonate solution (2×10 mL), brine (10 mL), dried over Na2SO4, filtered and concentrated to dryness under reduced pressure to give a yellow/brown solid. This was purified twice by Biotage chromatography (cyclohexane:ethyl acetate, gradient elution from 93:7 to 60:40) and then preparative HPLC (Method F) to give the desired product as a white solid (12 mg, 1.4% yield). 1H-NMR (500 MHz, CDCl3) δ 8.29 (1H, s), 7.16-7.41 (9H, m), 5.05 (2H, s), 5.02 (1H, br s), 4.44 (2H, s), 2.21-2.66 (4H, br m), 2.01-2.16 (1H, m), 1.74-1.88 (1H, m), 1.10-1.50 (9H, br m).
