Triethylamine → 3,5-Dichlorobenzyl 2-(2-((2-ethoxy-3,4-dioxocyclobut-1-en-1-yl)amino)ethyl)morpholine-4-carboxylate

A mixture comprising of 3,4-diethoxycyclobut-3-ene-1,2-dione (77 mg, 0.453 mmol) and triethylamine (253 μl, 1.813 mmol) in EtOH (1511 μl) was stirred at 40° C. for 20 minutes under nitrogen. After cooling to room temperature, 3,5-dichlorobenzyl 2-(2-aminoethyl)morpholine-4-carboxylate (step 2) (151 mg, 0.453 mmol) was added dropwise and the reaction mixture was allowed to stir at room temperature for a further 30 minutes. The resulting reaction mixture was concentrated under reduced pressure and diluted with EtOAc. The organic portion was washed with water, dried over MgSO4, filtered and concentrated under reduced pressure. The crude material was dried loaded using silica onto an ISCO 4 g column, eluting with 0-100% EtOAc in iso-hexane. The product fractions were concentrated under reduced pressure to afford the title compound;