Synthesis of 4-(Hydroxymethyl)dihydroisoindolium Salts and Their Intramolecular Recyclization

The review discusses intramolecular cyclization of ammonium salts containing a 4-hydroxybut-2- yn-1-yl group in combination with various π4-fragments, as well as mechanisms of cyclization and intramolecular recyclization of the resulting 4-(hydroxymethyl)dihydroisoindolium salts and their fused analogs. The process is accompanied by neither ring expansion nor contraction, and a pharmacophoric 1,3-dihydrofuran ring is formed instead of dihydroisoindolium fragment. The effects of electronic and structural factors on the intramolecular cyclization and recyclization processes are considered.