3-Amino-5-methylisoxazole was used in synthesis of:naphtho[1,2-e][1,3]oxazinesseries of 1-aryl-4-methyl-3,6-bis-(5-methylisoxazol-3-yl)-2-thioxo-2,3,6,10b-tetrahydro-1H-pyrimido[5,4-c]quinolin-5-ones, having potential mosquito larvicidal activityhydroxylamines of sulfadiazine and sulfamethoxazole