AlBr3-Mediated Tandem Cyclization-Carboxylation of Allenylbenzenes with CO2 in the Presence of Pyridines

Indene-2-carboxylic acids are prepared from allenyl-benzenes and CO2 by an AlBr3-mediated tandem reaction consisting of intramolecular Friedel-Crafts alkylation of allenylbenzenes and subsequent carbonation of the resulting indenylaluminum species. The reaction requires 2,6-di-tert-butylpyridine or 2,6-diiodopyridine to neutralize an acidic by-product without deactivating the Lewis acid.