Synthesis of 1,2,3-Triazole Substituted Isoxazoles via Copper (I) Catalyzed Cycloaddition

The synthesis of a series of 3,5-disubstituted isoxazole-4-carboxylic esters containing N-substituted 1,2,3-triazoles (V) starting from various benzaldehydes (I) is reported. Benzaldehydes undergo oximation with hydroxylamine hydrosulfate. Later, chlorination followed by condensation with methylacetoacetate and the hydrolysis of the resulting ester afforded respective carboxylic acid (II), which on chlorination with PCl5 gave the corresponding acid chlorides (III). The coraboxylic acid chlorides (III) on propargylation gave propargylic esters (IV) and these on click reaction gave the title compounds (V).