Acid-Enabled Dearomative Umpolung of 3-Indolylquinones toward C3-Oxygenated Benzofuro[2,3-b]indolines.

We report an acid-enabled dearomative umpolung of 3-indolylquinones for the synthesis of C3-oxygenated benzofuro[2,3-b]indolines. This transformation proceeds via an intramolecular annulation, initiated by acid-facilitated formation of a dearomatized iminium intermediate. The resulting o-quinone methide motif undergoes intramolecular cyclization to generate a C3-carbocation intermediate, which is subsequently trapped by nucleophiles. A variety of alcohols (including primary, secondary, monohydric, and diols) are compatible with this reaction, providing the corresponding products in moderate to good yields. The synthetic utility of this method is demonstrated by gram-scale synthesis and derivatization studies.