Halogenation with copper(II) halides. Halogenation of olefins with complexed copper(II) halides

Abstract

A new method for the halogenation of olefinic bonds without the utilization of molecular halogens is described. This synthetic technique is based on the reaction of olefins with copper(II) halides in the presence of strong coordinating agents. Simple olefins are converted to vicinal dihaloalkanes in good to excellent yields. Conjugated diolefins experienced predominately 1,4 addition. Complexed copper(II) halides in combination with different halide donors afforded an in situ synthesis of pseudohalogen compounds, which yielded ultimately chloroiodoand chlorobromoalkanes. The general scope of these reactions has been demonstrated for a variety

Catalytic, Stereoselective Dihalogenation of Alkenes: Challenges and Opportunities

“…220,221 The use of somewhat lower temperatures (70–80 °C) is possible in MeCN as the solvent, 224 but LiCl is usually added in these cases to solubilize the CuCl 2 and to further enhance the rate. 220,225 Chlorine has been deemed unlikely to be the active chlorinating agent in these reactions 221 as CuCl 2 is known not to decompose to CuCl and Cl 2 at these temperatures in the solvents employed 226 (albeit in the absence of olefins).…”

“…224 For example, the reactions of 2-butenes ( E )- 42 and ( Z )- 45 with CuBr 2 in MeCN at rt gives dibromides anti - 99 and syn - 100 , respectively, in 91% yield (w.r.t. CuBr 2 ) (Scheme 83).…”

“…224 In fact, the effectiveness of MeCN as a solvent for CuBr 2 -mediated dibrominations is attributed to its π-acidic character as a ligand. These results are interpreted as being a consequence of the disproportionation of CuBr 2 to CuBr and molecular bromine (i.e., CuBr 2 → CuBr + ½ Br 2 ), with “soft” or π-acidic ligands stabilizing the Cu(I) product and driving the equilibrium to the right.…”

CuX2-Mediated Halogenation of Alkylidenecyclopropanes: A Highly Efficient and Stereoselective Method for the Preparation ofZ-2, 4-Dihalobutenes

“…Considering the possibility of bromination of alkene in the presence of CuBr 2 [6], we used 2 equivalents of CuBr 2 as bromizating agent and luckily, (Z)-1-phenyl-2, 4-dibromobutene (2a) was obtained with high stereoselectivity in 52% yield. Further screening demonstrated anhydrous acetonitrile was more suitable reaction medium and the reaction could be carried out at the lower reaction temperature (65°C) affording a good yield of 2a (Scheme 4).…”

Versatile Reactivity and Catalytic Effects of Copper(II) Halides in Organic Syntheses

“…The halogenation of olefins has been studied in a variety of solvents [25,26]. Cyclohexene 23 was chlorinated or brominated to trans-1,2-dihalocyclohexanes 24 (Scheme 8).…”