Regioselective Addition of Grignard Reagents to Isoxazole-4,5-dicarboxylate Esters.

Regioselective mono-addition of a range of Grignard reagents with the 5-esters of 3-methylisoxazole-4,5-diesters affords 5-keto derivatives instead of tertiary alcohols which is explained by the complexing ability of the isoxazole oxygen atom and by the electron withdrawing effect of the isoxazole ring.