Aldehydes Switch Regioselectivity: a Prins Cyclization Strategy for the Synthesis of Indoline‐fused THFs and Indole‐fused Oxepanes

Abstract We have identified a switchable Prins cyclization process to form indoline‐fused tetrahydrofurans and indole‐fused oxepanes by applying different types of aldehydes under two sets of optimized conditions. Significantly, a novel Prins reaction mechanism involving an oxonium‐mediated rearrangement in the formation of five‐membered cyclic ethers is realized for the first time. magnified image