Diastereoselective synthesis of spiro[chromane-3,3′-indolines] and spiro[chromane-3,2′-indenes] via DBU promoted formal [4 + 2]cycloaddition reaction

Abstract A new DBU-catalyzed formal [4 ​+ ​2] cycloaddition between ortho-hydroxyphenyl-substituted para-quinone methides and electron-deficient dienophiles including 3-methyleneoxindoles and 2-aryldeneindene-1,3-diones was established. A wide range of functionalized spiro[chromane-3,3′-indolines] and spiro[chromane-3,2′-indenes] were successfully synthesized in good yields and with high diastereoselectivity. The features of the reaction included readily available substrates, mild reaction conditions, convenient methodology and good functional group tolerance.