Diethyl Oxalate → diisopropyl 3,4-dihydroxy-1-(4-methoxyphenyl)-1H-pyrrole-2,5-dicarboxylate

Participants

Reaction Conditions

Reaction Steps

Lithium isopropoxide (2M in THF) (10.4 mL, 20.8 mmol) was added to a mixture of diisopropyl 2,2′-((4-methoxyphenyl)azanediyl)diacetate (21) (2.69 g, 8.32 mmol) [prepared using the same procedure as Example B step (i) using isopropyl 2-bromoacetate] and diethyl oxalate (1.13 mL, 8.32 mmol), the mixture was stirred at 65° C. for 16 h. A further portion of lithium isopropoxide (2M in THF) (5.2 ml, 10.4 mmol) was added and the reaction stirred at 65° C. for 3 h. The reaction was quenched with acetic acid (5 mL) and the volatiles removed in vacuo, the crude product was took up in EtOAc (100 mL) and partitioned with water (100 mL), the aqueous was washed with EtOAc (2×100 mL) combined organics were washed with brine (150 mL), dried (MgSO4), filtered and solvents removed in vacuo to afford a brown oil. The crude product was recrystallised from hot i-PrOH (50 mL), to provide a white solid. The solid was purified by silica gel chromatography (12 g, 0-50% EtOAc in isohexane) to afford diisopropyl 3,4-dihydroxy-1-(4-methoxyphenyl)-1H-pyrrole-2,5-dicarboxylate (UL2-020) (21 mg, 1%) as a white solid: m/z 378 (M+H)+ (ES+). 1H NMR (400 MHz, DMSO-d6) δ: 8.62 (s, 2H), 7.12-7.01 (m, 2H), 6.93-6.84 (m, 2H), 4.80 (sept., J=6.3 Hz, 2H), 3.78 (s, 3H), 0.95 (d, J=6.2 Hz, 12H).

Provenance & Evidence