Oxone®‐Mediated Synthesis of Benzimidazoles from 1,2‐Phenylenediamines and Aldehydes: Preparation of 2‐(4‐Cyano‐Phenyl)‐1‐[2‐(3,4‐Dimethoxyphenyl)‐Ethyl]‐1H‐Benzimidazole‐5‐Carboxylic Acid Ethyl Ester