Preparation of chromane derivatives via indium-mediated intramolecular allylation reactions

Chromane is one of the common structural parts found in many natural products. We have already communicated the indium-mediated allenylation in one-pot fashion to construct chromane derivatives. We have felt that indium-mediated allylation is also worth investigating in order to find out not only the possible difference in reactivity between allyl indium vs. propargyl indium but also the stereoselectivity difference in the indium-mediated cycliztion. We here wish to disclose our results on the intramolecular indiummediated allylation to prepare chromanes. The substrate 2, a precursor for the cyclization, was prepared by the reaction of salicyladehyde (1) with 1,4dibromo-2-butene in the presence of potassium carbonate as a base and potassium iodide (catalytic amount) in acetone at room temperature (Scheme 1).