Halo-Jacobsen Rearrangement Induced by Steric Repulsion between peri-Iodo Groups

The naphthalene ring is distorted due to steric repulsion between iodo groups at the peri-positions. Due to the distortion, 1,8-diiodonaphthalene underwent a halo-Jacobsen rearrangement when treated with trifluoromethanesulfonic acid, producing 1,5-diiodonaphthalene and 1,4-diiodonaphthalene. In this reaction, acid-induced dehalogenative homocoupling also proceeded to form 4,4′-diiodo-1,1′-binaphthyl. The reaction selectivity could be controlled by varying the reaction temperature. DFT calculations and some control experiments revealed that these compounds were formed by different pathways.