NaHSO₄-SiO₂-Promoted Solvent-Free Synthesis of Benzoxazoles, Benzimidazoles, and Benzothiazole Derivatives

Table 2

Synthesis of 2-substituted benzoxazoles, benzimidazoles, and benzothiazoles^a.

Entry	Amines	Acid chlorides	Product	Yield (%)^b	M.P. (°C); reported (lit)	M.P. (°C); found^c
1				92	285–287^48	289–291
2				87	222–223^48	220–222
3				93	266–268^48	265–267
4				86	175–176^50	173–175
5				91	220–221^48	218–221
6				88	230–232^49	231–233
7				87	236–238^49	234–236
8				90	179–180^48	177–179
9				89	—	146–147
10				88	—	88–89
11				93	101–102^51	102–104
12				83	53–54^52	54–56
13				87	72–74^53	70–73
14				89	98–99^51	97–99
15				81	70–72^54	70–73
16				86	131–132^54	131–133
17				84	54–55^52	53–56
18				83	93–95^53	92–94
19				85	64–65^55	63–66
20				94	110–111^51	114–116
21				93	84–86^51	85–87
22				95	104–105^51	104–107
23				71	165–168^54	166–169
24				89	107–110^56	108–110
25				86	71–73^57	70–72

^aReaction conditions: 𝑜-phenylenediamine (1 mmol), benzoyl chloride (1 mmol), and NaHSO₄-SiO₂ (25%/wt) were stirred under solvent-free condition at 100°C for 12 h, ^b isolated yields, ^call products are solids.