Diiodoindium(III) Cation, InI2+, a Potent Yneophile. Generation and Application to Cationic Cyclization by Selective π‑Activation of CC

The removal of the iodide ion from indium triiodide by means of reactive Ag­(I) salts leads to the formation of the highly reactive ligandless cation InI2+, which is unusual in having two vacant low-lying p-orbitals. This bivalent Lewis acidity leads to an especially high affinity for the two orthogonal π-bonds of carbon–carbon triple bonds. Consequently, the double-coordinating InI2+ is an especially effective reagent for the selective activation of CC and the catalytic initiation of cationic cyclization processes. A number of such reactions are described to demonstrate synthetic utility.