Nitrogen → 2-[5-(2-Methyl-[1,3]dioxolan-2-yl)-thiophen-2-ylmethyl]-oxazole-4-carboxylic acid methyl ester

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Reaction Steps

In a flame dried round-bottomed flask equipped with a magnetic stir bar and under inert atmosphere (N2), hexamethylenetetramine (273 mg, 1.92 mmol) and DBU (0.29 mL, 1.92 mmol) were added to a stirred suspension of copper (II) bromide (429 mg, 1.92 mmol) in deoxygenated dry CH2Cl2 (2.0 mL). After 20 min, a deoxygenated solution of 2-[5-(2-methyl-[1,3]dioxolan-2-yl)-thiophen-2-ylmethyl]-4,5-dihydro-oxazole-4-carboxylic acid methyl ester (240 mg, 0.77 mmol) in CH2Cl2 (5.0 mL) was added and the reaction mixture was stirred at rt for 2 h. The solvent was removed under reduced pressure and the residue was partitioned between EA (60 mL), and 40 mL of a 1:1 mixture of sat. aq. NH4Cl and 25% aq. NH4OH. The aq. layer was extracted with EA (40 mL) and the combined organic layers were washed with 40 mL of a 1:1 mixture of sat. aq. NH4Cl and 25% aq. NH4OH followed by 10% citric acid (40 mL), sat. aq. NaHCO3 (40 mL) and brine (40 mL). The organic phase was dried over MgSO4, filtered, and the solvent was removed under reduced pressure. Purification of the residue by FC (2:1→1:4 hept-EA) gave the title compound as a pale yellow oil. TLC: rf (1:3 hept-EA)=0.40. LC-MS-conditions 01: tR=0.88 min, [M+H]+=309.98.

Provenance & Evidence