Mild arylboronic acid catalyzed selective [4 + 3] cycloadditions: access to cyclohepta[b]benzofurans and cyclohepta[b]indoles.

The first example of arylboronic acid catalyzed [4 + 3] cycloaddition reaction is reported. 3,5-Bis-(trifluoromethyl) phenylboronic acid is shown to be the best catalyst in this reaction. The method has also enabled the preparation of cyclohepta[b]benzofurans and cyclohepta[b]indoles in excellent yields.