Efficient synthesis of furoquinolinones using Hendrickson reagent-initiated cascade annulation

A new synthesis of furo[3,4-b]quinolin-3(1H)-one derivatives has been established in straightforward fashion in high overall yields. An efficient Hendrickson reagent-initiated cascade annulation, which is composed of mild conversion of the stable amide precursor to the reactive imido-carbonium intermediate and subsequent intramolecular aza Diels–Alder reaction, successfully serves as the key reaction in the synthesis. Final oxidative cleavage of the carbon–carbon double bond of representative tricyclic precursor 8g led to completion of the synthesis of quinoline-lactone 2g in a high yield.