BF 3 ·Et 2 O promoted selective synthesis of benzimidazoles

Benzimidazoles 3 , 6 and 9 have been synthesized selectively in excellent yields by cyclocondensation of β‐(3‐methyl‐5‐styryl‐4‐isoxazolyl amido) benzoic acids, acrylic acids and propionic acids with 1,2‐phenylene diamines by employing BF 3 ·Et 2 O as the catalyst. When the same reaction was carried out in pyridine it resulted in mixture of products in each case ( 3 & 4 , 6 & 7 and 9 & 10 ). Other methods tried by using polyphosphoric acid, HCl, TFA also led to mixtures of 3 & 4 , 6 & 7 and 9 & 10 in each case, similar to that of pyridine reaction.