Alkenes dichlorination

Despite tremendous advances in the development of chiral methods, asymmetric alkene dichlorination remains one of the challenges. This reaction was successfully achieved for frans-cinnamyl alcohols as substrates using (dichloroiodo)arenes in combination with dimeric cinchona alkaloid derivatives 41 leading to products with up to 85% ee (Scheme 19) [64]. Chiral iodine(V) reagent 42 in combination with pyridine hydrobromide led to the dibromination of p-methylstyrene in only 3% ee [65]. 

Boyes and Wild reported the manganese-mediated regioselective chlorination of allenes [14]. For the dichlorination of cyclo-l,2-nonadiene, the dichloride was obtained as the major product whereas the reaction of monosubstituted allene afforded a mixture of regiosomers of the dichlorination products with 2,3-dichloro-1-alkene 12 being the major one. The yield with oxalyl chloride is better than that with TMSC1. 

Selected examples of dichlorination of alkenes and alkynes using TBA-ICL in the dark... 

The ene- pe chlorination, specific with this halogen atom, of alkenes would account for a somewhat different mode of halogen addition, giving usefiil allylic dilorides. Efficient and convenient reagents and methods develtqted are dichlorine monoxide (ChO equation 36), r-butyl hypochlorite, and electro-chemical reactions with chloride ion (equation 37). The ene-type chlorination proceeds smoothly with... 

In 1997, Marko and co-workers (423) followed up on their initial report of the KMn04 and oxalyl chloride system. This new system consists of KMn04, MesSiCl, benzytriethylammonium chloride with dichloromethane as the solvent. It gives good delds of dichlorinated alkenes. The permanganate anion is brought into solution by the ben-... 

Dichlorination of cyclopentane under free-radical conditions is not a realistic approach to the introduction of two chlorines in a trans-1,2 relationship without contamination by isomeric dichlorides. Vicinal dichlorides are prepared by electrophilic addition of chlorine to alkenes. The stereochemistry of addition is anti. 

Addition to double bonds. Dichlorination of alkenes with RuCl2(PPh3)3 and -exachloroethane does not affect other functional groups. However, the reaction is rerformed in a sealed tube in hot toluene. 

Chlorination of Alkenes. A novel stereospecific dichlorination of electron rich alkenes has been reported using a manganese reagent generated from Benzyltriethylammonium Chloride and oxalyl chloride (eqs 13-17). No oxygenation b)q)roducts are observed. 

The potential of chiral sulfonium reagents to affect asymmetric halo-nium ion addition to alkenes was studied by Snyder et al. (13S1886). Although racemic dihalogenation and halohydroxylation of alkenes are well known, the corresponding enantioselective variants have remained elusive. Snyder first prepared a series of chiral, crystalline, sulfur-derived halonium reagents and indeed was able to carry out enantioselective dichlorination and iodohydroxylation of 1,2-dihydronaphthalene. Other chiral sulfonium reagents and the scope of the reaction and reaction conditions were also extensively studied. 

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