The Brønsted acid-promoted dimerization of o-alkynylbenzaldehydes has been discovered and studied in the presence of 45% aq. HBF4 in acetic acid. The developed cascade methodology provides a convenient one-step synthesis of symmetrical 2,3,6,7-dibenzo-9-oxabicyclo[3.3.1]nona-2,6-diene (Kagan's ether) analogues bearing various functionalities.
