Novel brønsted acid-catalyzed Michael-type Friedel-Crafts reactions of indoles and acetalization of aldehydes

The first example of 2,6-pyridinedicarboxylic acid (PDA)-catalyzed organic reactions was developed in this article. The special bifunctional brønsted acid could be used in the chemoselective acetalization of aldehydes for preparation of corresponding acetals in excellent yields, and the Michael-type Friedel-Crafts reactions of indoles with α,β-unsaturated enones were also promoted by the same catalyst efficiently.

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