Sulfonic Acid Functionalized Nano-γ-Al₂O₃: A New, Efficient, and Reusable Catalyst for Synthesis of 3-Substituted-2H-1,4-Benzothiazines

Table 1

Catalyst optimization for the synthesis of 3-phenyl-2H-1,4-benzothiazine^a.

Entry	Catalyst	Mg/mmol	Time/h	Yield/%^b
1	—	—	24	42
2	Sulfonic acid functionalized nano-γ-Al2O3	25	4	81
3	Sulfonic acid functionalized nano-γ-Al2O3	50	3	96
4	Sulfonic acid functionalized nano-γ-Al2O3	100	3	96
5	Sulfonic acid functionalized nano-γ-Al2O3	150	3	95
6	Nano-γ-Al2O3	50	24	53
7	p-TsOH	50	5	79
8	Sulfamic acid	50	5	81
9	Silica sulfuric acid	50	6	82

aReaction conditions: o-aminothiophenol (1 mmol), 2-bromo-1-phenyl-ethanone (1 mmol); EtOH (10 mL); reflux.
bIsolated yield.