Optimization of reaction conditions of 1a with NH₂OH·HCl mediated by BF₃·OEt₂ to access 3,4-disubstituted isoxazole 4a regioselectively^a.

Entry	i			Ratiob (%)				Yieldc (%)
	Solvent	BF3·OEt2 (equiv.)	Time (h)	2a	3a	4a	5a
1	MeCN	0.5	18	37	13	50	—	—
2	MeCN	1.0	20	22	8	70	—	—
3	MeCN	1.5	24	9	—	81	10	—
4	MeCN	2.0	24	—	—	90	10	79
5 d	MeCN	2.0	5	—	—	90	10	79
6d	EtOH	2.0	2	64	36	—	—	—

^aReaction conditions: 1a (0.5 mmol), NH₂OH·HCl (0.6 mmol, 1.2 equiv.), room temperature, solvent (4 mL).

^bCalculated from the ¹H-NMR spectrum of crude product.

^cIsolated yield (regioisomeric mixture).

^dPyridine (1.4 equiv.).