BMC Chemistry

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	R^a	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]

4a-s are the synthesized tetrahydrobenzo[b]pyrans with different R
^aReaction conditions: malononitrile (1 mmol), aldehyde (1 mmol), dimedone (1 mmol) and nano-SiO₂/DBN (0.03 g)
^bIsolated yield
^cDecomposed

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