A rapid, sustainable and environmental friendly protocol for the catalyst-free synthesis of 2-methyl-5-oxo-hexahydroquinoline-3-carboxylate via ultrasonic irradiation

•An efficient method using ultrasound irradiation.•Synthesis of novel 2-methyl-5-oxo-hexahydroquinoline-3-carboxylate quinoline derivatives.•One-pot/multi-component green solvent (ethanol) protocol.•Excellent yields (92 to 98%) in short reaction times (< 10 min).