Regioselective Synthesis of Substituted Tetrahydrofurans through Prins Cyclization

The synthesis of functionalized tetrahydrofurans was accomplished through the TfOH-catalyzed Prins cyclization. The reaction proceeded regioselectively at the internal alkene carbon in the presence of catalytic amounts of TfOH to afford the five-membered ring, rather than the typical six-membered ring. Another attractive feature of this protocol is the metal catalyst-free characteristic of the cyclization process.