SYNTHESIS OF ISOXAZOLES BEARING METHOXYCARBONYL AND FORMYL GROUPS BY 1,3-DIPOLAR CYCLOADDITION OF NITRILE OXIDES TO OLEFINIC AND ACETYLENICDIPOLAROPHILES

The 1,3-dipolar cycloadditions of benzo-, bromoformo- and acetonitrile oxides to enamino ester (1) and acetylenic esters (2, 3) afforded fun ctionalized isoxazoles in moderate to good yields. Cycloadditions with the enamino ester (1) gave the corresponding methyl 5-dimethoxymethyl isoxazole-4-carboxylate (7a-9a) as the sole regioisomer, whereas the r eactions with acetylenic dipolarophiles (2, 3) were generally less sel ective and the regioselectivity depended significantly on the nature o f the substituents of the dipole and the acetylenic ester.