TfOH-Catalyzed Cascade Reaction: Metal-Free Access to 3,3-Disubstituted Phthalides from o-Alkynylbenzoic Acids

A facile new method for the synthesis of 3,3-disubstituted phthalides is reported. A successive reaction process begins with the TfOH-catalyzed cyclization of o-alkynylbenzoic acids followed by an ortho-regioselective electrophilic alkylation of various electron-rich aromatic compounds or alkenes, which has been successfully developed. The corresponding regioselective products of 3-substituted phthalide were obtained in good to high yields.