An efficient and rapid procedure for the N‐alkyl enamination from thioketones to push–pull (E/Z)‐enamine derivatives is reported. The starting thioketone 2 was obtained by regioselective thionation of 3‐benzoylpyrrolo[2,3‐b]quinoxalin‐2‐one (1) with Lawesson's reagent (LR). 1H NMR and X‐ray crystal structure analyses of 1‐aryl‐3‐(alkylaminophenylmethylidene)pyrrolo[2,3‐b]quinoxalin‐2‐ones 3–6 confirmed that the E diastereoisomers predominated. Interconversion of the isolated E form of 3b and 4a into the Z configuration and their E/Z equilibria in [D6]DMSO were studied by temperature‐dependent 1H NMR spectroscopy. The photophysical properties of compounds 1–6 are also reported. We found that the non‐fluorescent compounds 3a–6a are chemosensors for the zinc ion. Fluorescent titrations of these sensors with zinc(II) acetate showed that compound 6a has the best working range of zinc concentrations with Kd = 3.77 00 ± 0.51 μM.