Unsymmetrization of 1,8-Dibromonaphthalenes by Acid-Induced Halogen Dance Reaction

A simple and powerful tool for preparing uncommon bromoarenes via the unsymmetrization of a naphthalene ring was developed. The steric repulsion between the peri-bromo groups of 1,8-dibromonaphthalene distorts the naphthalene ring, allowing for nonelectronical activation. Ring distortion facilitates the 1,2-rearrangement of the bromo group, affording 1,7-dibromonaphthalene upon treatment with trifluoromethanesulfonic acid (halogen dance reaction). For 1,4,5,8-tetrabromonaphthalene, stepwise 1,2-rearrangements proceeded successively to furnish 1,3,5,7-tetrabromonaphthalene. Density functional theory calculations suggest that this reaction is initiated by ipso-protonation, with a subsequent 1,2-rearrangement occurring via the bromonium transition state. Utilizing 1,7-dibromonaphthalene, which is characterized by two C-Br bonds arranged at a 60° angle, a unique metal-organic framework comprising a 52-membered ring network was synthesized.