Substituent Effect on the Ring Transformation of 4- (Di/trisubstituted phenyl) -3, 5-bis (methoxycarbonyI) -2-isoxazoline 2-Oxidest

Abstract

4- (Di/tri-substituted phenyl) -3, 5-bis (inethoxycarbonyl) -2-isoxazoline 2-oxides [3] were synthesized from di/tri-substituted benzaldehydes and methyl nitroacetate in reasonable yields. The substituents R of [3] inyolve chloro, methoxyl, and methylenedioxy groups (Fig.1and Tables 1, 2).
The ring tran sformation of [3] were executed by promotion of TiC14 in dichloromethane giving either 3 H-indole-3-acetate 1-oxide of type [4] or benzofuro[3, 3 a-d]isoxazole-3, 4dicarboxylate of type [6]/[7]. Di/trimethoxyphenyl derivatives [3e] and [3h] were transformed into 3a, 4-dihydro-5aH-benzofuro[3, 3 a-d]isoxazol-7 (6H) -ones [7e] and [7h] in good yields (Fig.2).
The substituents R strongly affected the course of the reaction such that ipso site-activating group, e. g. [3b], [3e] and [3h] exclusively afforded the respective benzofuro[3, 3 a-d] isoxazoles; whilst the both ortho and ipso sites-activating group such as [3a] and [3c] preferably provided 3 H-indole-3-acetate 1-oxides along with a by-product [8c]. However, ortho site-activating [3d] and [3i] were recovered unexpectedly under the similar reaction conditions (Table 3).