BrCl, with alkenes

Addition of XY to alkenes can also be accomplished by indirect means. Buckels and Long used N-bromoacetamide and HCl to add BrCl to alkenes. The stereochemistry of the reaction suggested an anti addition, which was consistent with attachment of Br" " from protonated N-bromoacetamide to give a bromonium ion (or / -bromocarbocation), followed by attachment of Cl. Reaction of N-bromoacetamide and HF in a proton-accepting solvent such as THF (which increases the solubility of HF) gave anti addition of FBr to cyclohexene. Similarly, reaction of cyclohexene with N-iodoacetamide and HF produced trflns-l-fluoro-2-iodocyclohexane. ... 

Reaction of alkenes with BrCl proceeds via the intermediate [alkene-Br]+ rather than the intermediate [alkene-Cl]+. Explain using a two-orbital interaction diagram. (The structure of the complex between ethylene and BrCl in the gas phase has been determined by microwave spectroscopy. It is T-shaped, with the BrCl molecule lying perpendicular to the ethylene plane and pointing bromine-end first toward the midpoint of the C=C bond Legon, A. C. Bloemink, H. I. Hinds, K. Thorn, J. C., Chem. Eng. News, 1994 Nov. 7, 26-29.)... 

The full paper on the reactions of iodine(l) thiocyanate and 5a-androst-2-ene and other alkenes has appeared." An investigation into the stereochemistry of the addition of BrCl to cholesterol revealed that the ratio of a /8 attack was 4.5 1, which was higher than that for other electrophilic additions. It was suggested that the reaction involved rapid reversible formation of the bromonium ions followed by attack by chloride ion and that the opening of the 5/8,6/3-bromonium ion was slow relative to that of the 5a,6a-bromonium ion owing to steric interactions with the la-, 3a-, 7a-, and 9a-axial hydrogen atoms. 

The reaction of an ot-halo sulfone with a base to give an alkene is called the Ramberg-Backlund reaction The reaction is quite general for a-halo sulfones with an ot hydrogen, despite the unreactive nature of a-halo sulfones in normal Sn2 reactions (p. 486). Halogen reactivity is in the order I > BrCl. Phase-transfer catalysis has been used. " In general, mixtures of cis and trans isomers are obtained, but usually the less stable cis isomer predominates. The mechanism involves formation of an episulfone, and then elimination of SO2. There is much... 

The mixed halogens ICl, IBr, and BrCl also add to alkenes. White and Robertson found third-order kinetics for the reaction and determined the relative reactivities to be BrCl > ICl > Br2 > IBr > l2- The l ge reactivity of BrCl means that addition of BrCl can occur when alkenes react with mixtures of Br2 and Cl2. The regioselectivity of addition of mixed halogens was reported by Ingold and Smith. Addition of ICl to propene gave 69% of 2-chloro-l-iodo-propane (30) and 31% of l-chloro-2-iodopropane (31), and addition to styrene gave more than 95% of l-chloro-2-iodo-l-phenylethane. ... 

Several papers have appeared describing the synthesis of alkyl halides from organoboranes. Alkyl chlorides are obtained by the reaction of trialkylboranes with dichloramine-T, and in somewhat lower yield with iV,N-dichlorourethane/ whereas alkyl bromides are produced in excellent yield when the boranes derived from terminal alkenes and dicyclohexylborane are treated with either Bt2 or BrCl. Alkyl iodides are obtained from the same boranes by the use of ICl-NaQAc " or iodide ion-chloramine-T/ and this latter method has been applied to the radioiodination of olefins (with Vinyl iodides result from... 

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