Expedited Synthesis of Benzofuran-2-Carboxylic Acids via Microwave-Assisted Perkin Rearrangement Reaction.

3-Halocoumarins are readily converted into benzofuran-2-carboxylic acids via a Perkin (coumarin-benzofuran ring contraction) rearrangement reaction. This rearrangement entails initial base catalyzed ring fission. The resulting phenoxide anion then attacks a vinyl halide to produce the final benzofuran moiety. We explored this reaction under microwave reaction conditions and were able to significantly reduce reaction times as well as obtain very high yields of a series of benzofuran-2-carboxylic acid derivatives.