AbstractThe reactivity of the β‐enamino ketones, 3‐amino‐1‐(p‐phenyl‐substituted)‐2‐buten‐1‐ones 1a‐d and β‐enamino esters, ethyl 3‐amino‐3‐(p‐phenyl‐substituted)‐2‐propenoates 5a‐d was systematically studied when allowed to react with hydrazine and methylhydrazine under solid support K‐10/ultrasound conditions and in homogeneous media (reflux in ethanol or dichloromethane). The products were pyrazoles 2a‐d, N‐methylpyrazoles 3a‐d, 4a‐d and N‐methylpyrazolinones 6a‐c and 7a‐c. The regiochemistry of the cyclization reactions showed dependence upon the reaction conditions employed as well as upon the sub‐stituent in the aromatic ring.