Synthesis of Indenes by a BF3·OEt2-Mediated, One-Pot Reaction of Aryl Homopropargyl Alcohols, Aldehydes, and Arenes.

A new and efficient protocol to prepare indenes is reported. Assisted by boron trifluoride diethyl etherate, the one-pot reaction of aryl homopropargyl alcohols and aldehydes in the presence of arenes yielded indene derivatives. The reaction was studied with various substrates, which suggests a cascade reaction including a sequence of Prins, Friedel-Crafts, ring-opening reactions, and Friedel-Crafts to form three C-C bonds leading to indenes.