Comparison of the electrophilic and free-radical addition of halogens with hexafluoro-1,3-butadiene and 1,3-butadiene

Ionic and photochemical reaction of chlorine (Cl₂), bromine (Br₂) and iodine monochloride (ICl) to hexafluoro-1,3-butadiene (1) and 1,3-butadiene (2) were carried out under conditions that would provide product distributions under controlled ionic or free-radical conditions. Product distributions for ionic reaction of Cl₂ and Br₂ with 1 are similar and suggest a weakly-bridged halonium ion species. Theoretical calculations support weakly-bridged chloronium and bromonium ions for both dienes 1 and 2. There are more of the 1,4-dihalo-2-butene products from ionic halogenation of 1 than 2 which correlates with the greater charge density on carbon-4 of halonium ions from 1. Ionic and free-radical reactions of ICl with 1 give 8 and 2% of 3-chloro-4-iodohexafluoro-1-butene and 4-chloro-3-iodohexafluoro-1-butene, respectively. The minor cis-1,4-dihalo-2-butene products from 1 and 2 are reported when formed.     

Rearrangement of 3-membered 1,1,2-trifluorobromonium and iodonium ions and comparison of trifluorochloronium to fluorocarbenium ions

Reactions of chlorine (Cl(2)) 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.     

Reaction of methyl hypochlorite with certain olefins in the presence of boron trifluoride

Fluoro chlorides are major products in the reaction of methyl hypochlorite with certain olefins in the presence of boron trifluoride.     

Ionic and radical addition of chlorine,bromine and some halogen systems of butadiene monoxide (4)

Ionic reactions of bromine, chlorine, methyl hypochlorite or N-bromosuccinimide with butadiene monoxide ( 4 ) give only 1,2-addition products. The Markownikoff (1-halo-2-methoxy-3,4-epoxybutane) and anti-Markownikoff (2-halo-1-methoxy-3,4-epoxybutane) product ratios for ionic reaction of methyl hypochlorite and N-bromosuccinimide in methanol with 4 are similar to those obtained with 1-hexene. These data indicate that a rather symmetrical halonium ion is formed in the ionic halogenation of 4 . Free radical reaction of bromine, chlorine, or trichloramine to 4 does not give ring-opened products as one might expect for formation of an epoxy carbonyl intermediate. The mechanistic implications from these observations are discussed.     

Reaction of halogens with some α,β-unsaturated aldehydes and ketones

Mechanisms are proposed to account for evidence indicating that some simple α,β-unsaturated aldehydes and ketones do not react with halogens by the expected attack on the CC bond.     

Boron trifluoride promoted reactions of n-haloelectrophiles with alkenes

N-Haloelectrophiles react with alkenes in the presence of boron rifluoride etherate to give halofluorides and N-halo adducts.