A series of novel sulfamethoxazole derivatives were synthesized using the appropriate route. The 4-((4-amino-2,5-dimethyiphenyl) diazenyl)-N-(5-meth-ylisoxazol-3-yl) benzene sulfonamide was synthesized using SMX 1 as diazonium component via diazotization reaction by NaNO2/HCl. The diazonium salt thus obtained was coupled, using the standard experimental procedure, to a range of 2,5-dimethylaniline to afford the requisite azo dye in good yield. The Schiff base derivatives were obtained by the condensation reaction of a compound 2 with various aldehydes to give compounds 3a-f, which undergo [2+2] cycloaddition reaction with chloroacetyl chloride to produce substituted β-lactam derivatives 4a-f.