New versatile syntheses of 3-aminoisoxazoles and their derivatives are described. 3-(N, N-Disubstituted amino) isoxazoles 5 were synthesized by heating 3-chloro-2-methylisoxazolium chlorides 1 with secondary amines, or by the substitution reaction of 1 with primary amines, followed by the dehydrochlorination and the subsequent addition-elimination reaction of alkyl or acyl halides with the resulting imines 6. Among the products 5, 3-(N-substituted acetylamino) isoxazoles were hydrolyzed with base to give 3-(N-monosubstituted amino) isoxazoles 3. 3-Aminoisoxazoles 7 were synthesized by the reaction of 1 with potassium phthalimide, followed by treatment with hydrazine.
Heteroaryl amines readily undergo Buchwald-Hartwig amination reactions with a range of aryl and heteroaryl bromides at room temperature using t-BuXPhos Pd-precatalyst and NaOt-Bu. The pharmaceutically attractive biaryl amines are generally formed in short reaction times (0.5-16 h) and in good to excellent yields.