Rearrangement of 3-Membered 1,1,2-Trifluorobromonium and Iodonium Ions and Comparison of Trifluorochloronium to Fluorocarbenium Ions

• Published in: Journal of organic chemistry Vol. 73; no. 12; pp. 4532 - 4538
• Main Authors: Shellhamer, Dale F, Davenport, Kevyn J, Forberg, Heidi K, Herrick, Matthew P, Jones, Rachel N, Rodriguez, Sean J, Sanabria, Sunamita, Trager, Nicole N, Weiss, Ryan J, Heasley, Victor L, Boatz, Jerry A
• Format: Journal Article
• Language: English
• Published: Washington, DC American Chemical Society 20-06-2008
• Subjects: Aliphatic compounds; Chemistry; Exact sciences and technology; Organic chemistry; Preparations and properties; Chemical rearrangement; Five membered ring; Organic cation; Chlorination; Quantum chemistry; Molecular structure; Chlorine; Three membered ring; Theoretical study; Organic halogen compounds; Alkene; Carbenium compounds; Halogen compound; Iodonium compounds; Vinylic compound; Chloronium compounds; Bromonium compounds; Fluorine Organic compounds; Ethylenic compound; Comparative study; Iodine; Nucleophile
• ISSN: 0022-3263; 1520-6904
• DOI: 10.1021/jo800472e

Reactions of chlorine (Cl2) with 4-halo-1,1,2-trifluorobut-1-enes (1, 2, or 3) give open-ion intermediates A and E that are in equilibrium. The open-chloronium ions (E) rearrange to a five-membered-ring halonium ion during ionic chlorination of 3 when the number-4 halo-substituent is iodine. Three-membered-ring bromonium and iodonium ions from alkenes 1, 2, or 3 are rather symmetrical and similar in structure. Quantum chemical calculations show that five-membered-ring halonium ion intermediates are 11 to 27 kcal/mol more stable than the three-membered-ring halonium ions or the open-ions A and E. The five-membered-ring intermediates lead to rearranged products. Rearranged products increase as the number-4 halogen (Z) becomes more nucleophilic (Z: Cl < Br < I). Open chloronium ions from ionic chlorination of terminal fluorovinyl alkenes are compared to the open ions generated by protons to similar alkenes.