An approach for the construction of furo[3,2-]quinolines and furo[2,3-:4,5-]diquinolines is developed through a metal-free [4 + 2] cycloaddition of easily available in situ generated aza--quinone methides and furans. The reaction tolerates a wide range of aza--quinone methides and substituted furans to afford the corresponding dihydro- or tetrahydrofuroquinolines in good to excellent yields. Mechanistic studies reveal that the reaction involves a concerted [4 + 2] cycloaddition pathway and shows a high regioselectivity of cycloaddition for a furan ring. The present method features mild reaction conditions, dearomatization of furans, high regio- and diastereoselectivity, gram-scalable preparations, and diversity of furoquinolines.
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