Synthesis of Various Schiff Bases Containing Isoxazole Ring and Their Applications with Thioglycollic Acid and Diverse Phosphorus Reagents

Abstract

A series of Schiff bases bearing isoxazole and pyrazole rings were synthesized. Application of thioglycollic acid on two selective synthesized Schiff bases afforded the corresponding thiazolidin‐4‐one derivatives. On the other hand, following the multicomponents one‐pot Kabachnik– Fields reaction, the Schiff base generated in situ from 4‐chlorobenzaldehyde and 5‐methyl isoxazol‐3‐amine was trapped by phosphorus reagents to produce the corresponding amino phosphonates in moderate yields. However, the latter products could also be obtained in better yields (≥78%) by directly applying the dialkylphosphites to a selective synthesized Schiff base. Similarly, a series of α‐aminophosphonates could be obtained from 5‐chloro‐3‐methyl‐1H‐pyrazol‐4‐carbaldehyde, 5‐methylisoxazol‐3‐amine, and phosphorus reagents. Moreover, applying hexaalkyl triamido phosphites to the N‐(4‐chlorobenzylidene)‐5‐methylisoxazol‐3‐amine in ethanol afforded methylphosphonic diamide derivatives, whereas N‐((5‐chloro‐3‐methyl‐1H‐pyrazol‐4‐yl)methylene)‐5‐methylisoxazol‐3‐amine underwent dechlorination through reaction with hexaalkyl triamido phosphites to give the respective amine derivatives.