A green protocol for the rapid synthesis of pyrimido-quinoline derivatives

A very simple yet efficient approach has been developed for the synthesis of pyrimido[4,5-b]quinoline derivatives. The three-component condensation of dimedone (1 eq.) with aromatic aldehydes (1 eq.), and 6-amino-1,3-dimethyluracil (1 eq.) by a Brønsted acidic ionic liquid catalyst, namely 1,4-Bis(pyridinium bi-sulfonic acid)benzene dimethylsulfonate (BPBSBDM) produced the mentioned derivatives in short reaction times (8–18 min) with high yields (90–98%). The optimal reaction conditions included the use of 6 mol% catalyst in water solvent at a mild temperature of 50 °C. The two functional groups acidic (sulfonic acid) and weak basic (mesylate) give this catalyst a dual acidic-basic nature, which supports its high performance as shown in the proposed mechanism. The BPBSBDM offered significant reusability as a homogeneous catalyst for four cycles with negligible reduction in catalytic activity. The considerable values of turnover number (TON) and turnover frequency (TOF), simple work-up, the introduction of novel derivatives to the literature (1 k to 1n), easy and cost-effective synthesis of catalyst, the green nature of the reaction, and the comprehensiveness of the protocol in facile production of various derivatives are other attractive aspects of our method.

Graphical Abstract