An abnormal regioselective substitution of 2-indolylmethanols with nucleophiles such as cyclic enaminone and cyclic anhydride has been established in the presence of Brønsted acid, which efficiently afforded C3-functionalized indole derivatives with structural diversity in high yield and regiospecificity (40 examples, up to 99% yield). Using this approach, the reactivity of the C3-position of the indole was switched from nucleophilic to electrophilic, which could serve as an "umpolung" strategy in organic synthesis.
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Li et al. (2016) studied this question.