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Table 3 Synthesis of tetrahydrobenzo[b]pyran in the presence of nano-SiO2/DBN at 60 ºC in H2O/EtOH (1:1)a

From: Nano-SiO2/DBN: an efficacious and reusable catalyst for one-pot synthesis of tetrahydrobenzo[b]pyran derivatives

Entry Ra Product Time (min) Yield (%)b M.P (°C) found M.P (°C) reported (refs.)
1 C6H5- 4a 20 85 232‒234 234‒235 [22]
2 4-Cl-C6H4- 4b 15 92 214‒216 215‒216 [22]
3 2-Cl–C6H4- 4c 35 81 217‒218 218‒219 [23]
4 2,6-Cl2-C6H3- 4d 50 79 245‒247 250‒252 [23]
5 4-NO2-C6H4- 4e 15 89 181‒183 181‒182 [27]
6 3-NO2-C6H4- 4f 20 91 215‒217 217‒218 [27]
7 2-NO2-C6H4- 4 g 35 80 232‒234 233‒234 [22]
8 4-Br-C6H4- 4 h 30 89 199‒201 197‒201 [13]
9 4-F-C6H4- 4i 40 91 192‒194 191‒193 [15]
10 4-CN-C6H4- 4j 25 85 231‒233 226‒228 [24]
11 4-OCH3-C6H4- 4 k 25 70 208‒210 208‒212 [23]
12 3,4-(OCH3)2-C6H3- 4 l 50 82 175‒176 206‒208 [25]
13 4-OH-C6H4- 4 m 40 78 217‒219 214‒216 [23]
14 4-(CH3)2CH-C6H4- 4n 30 90 197‒199 203‒207 [13]
15 4-CO2CH3-C6H4- 4o 15 78 257‒259 259‒260 [27]
16 1,4-Phenylene 4p 50 91 285 (d)c 270 (d) [26]
17 2-Furyl- 4q 25 84 216‒218 217‒219 [23]
18 Pentyl- 4r 20 83 162‒164 164‒165 [27]
19 Styryl- 4 s 30 90 217‒219 218‒218 [23]
  1. 4a-s are the synthesized tetrahydrobenzo[b]pyrans with different R
  2. aReaction conditions: malononitrile (1 mmol), aldehyde (1 mmol), dimedone (1 mmol) and nano-SiO2/DBN (0.03 g)
  3. bIsolated yield
  4. cDecomposed