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20. When 1 g of 1,2-phenylenediamine (1a) was used as a scale-up
experiment, 2-phenylbenzimidazole (3aa) was obtained in 26%
yield without further optimization.
21. Typical procedure: A Typical example of the synthesis of
benzimidazole (Table 2, entry1). A solution of 1,2-
benzenediamine (1a, 0.15 mmol) and benzaldehyde (2a, 0.15
mmol) in dry EtOAc (3 mL) in a Pyrex test tube was stirred under
an argon atmosphere for 30 min. Then magnesium iodide (0.0075
mmol) in dry EtOAc (2 mL) was added, and stirred and irradiated
externally with a fluorescent lamp for 6 h with an O2 balloon. The
reaction mixture was concentrated under reduced pressure, and
purification of the crude product by PTLC (CHCl3 : MeOH= 98 :
2) provided benzimidazole (3aa) (Rf = 0.6, 27.1 mg, 93%).
22. We cannot rule out that MgI2 also works as a Lewis acid because
MgI2 gave slightly higher yield than that of I2.
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