Isobutyryl chloride → Methyl 5-isopropyloxazole-4-carboxylate

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To a solution of sodium methoxide (1.86 g) in DMF (30 ml) was added methyl isocyanoacetate (2.38 ml) dropwise at −50° C. and the mixture stirred for 30 min at −50° C. 2-Methylpropanoyl chloride (3.36 ml) was added gradually to the mixture at −50° C. and the mixture stirred for 2 h at −50° C. The mixture was diluted with DCM (50 ml) and saturated sodium bicarbonate solution (50 ml) was added and the organic layer collected using a hydrophobic frit. The aqueous layer was washed with DCM (2×50 ml) and separated by hydrophobic frit. The combined organic phases were concentrated in vacuo. This was purified by chromatography on silica gel, eluting with a gradient of 0-100% ethyl acetate in cyclohexane, followed by 0-20% methanol. The residue was distilled using a Kugelrohr to give the title compound (553 mg) as yellow solid.

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