Stereoselective synthesis of 3-(ethoxycarbonyl)-4-hydroxy-5-(1-hydroxyalkyl)-2-isoxazoline 2-oxides by reaction of 2,3-epoxy aldehydes and ethyl nitroacetate on alumina surface

Abstract

Treatment of racemic 2,3-epoxy aldehydes and ethyl nitroacetate with alumina affords title compounds through a nitroaldol reaction—cyclization process. While in the case of 3-trans-monosubstituted substrates, C4,C5-trans and cis isomers (dr = 1.5) with C5,C6-anti configuration are obtained, 3-cis-monosubstituted 2,3-epoxy aldehydes give C4,C5-trans and cis derivatives with a much higher diastereoselectivity (dr > 20) and C5,C6-syn configuration. 5-Exo cyclization occurs also when 2,3-epoxy aldehydes are 2-substituted.