A formal [3 + 2] cyclization reaction of 3‐(2‐oxo‐2‐arylethylidene)indolin‐2‐ones and amidines has been developed, regioselectively affording a series of new 3‐(imidazol‐4‐yl)indolin‐2‐ones in good to excellent yields. The reaction was easily conducted in ethylene glycol using Cs2CO3 as a base promoter under microwave irradiation. Flexible structural modification, and broad functional group compatibility as well as mild reaction conditions make this strategy a useful and attractive process of library generation for drug discovery.