Pentafluoropropionic Acid: An Efficient and Metal-Free Catalyst for the One-Pot Synthesis of Tetrahydrobenzo[b]pyran Derivatives

Table 3

Comparison of efficiency of various catalysts in synthesis of tetrahydrobenzo[b]pyrans.

Entry	Catalyst	Conditions	Time (min)	Yield (%)	Reference
1	Trisodium citrate	EtOH–H2O; reflux	5–120	80–96	[14]
2	Na2SeSO4	EtOH–H2O; reflux	30–180	85–98	[12]
3	PPA-SiO2	H2O; reflux	8–15	77–93	[15]
4	Caro’s acid-SiO2	EtOH–H2O; reflux	15–20	92–95	[13]
5	ZnO-beta zeolite	EtOH; reflux	35–52	86–95	[10]
6	NaBr	MW; 70–80°C	10–15	85–95	[11]
7	TBAB	EtOH; reflux	20–140	87–95	[28]
8	NaOCl	Grinding	10–30	80–88	[19]
9	Ce1Mg𝑥Zr1−𝑥O2	EtOH; reflux	35–45	90–94	[22]
10	Supported polyamine	EtOH–H2O; reflux	120–220	88–95	[23]
11	Urea-ChCl	80°C	60–240	75–95	[24]
12	TMAH	H2O; r.t.	30–120	80–92	[26]
13	PFPA	EtOH–H2O; r.t.	60–80	89–92	This work