Radical additions copper® chloride

In the presence of copper(I) chloride, FC-113a adds to silyl enol ethers affording adducts which can be transformed into the /1-chloro-/i-trifluoromethyl enones in moderate yields [100]. The carbon-carbon bond is formed via a free radical addition reaction (Eq. 28). Free radical addition mediated by iron pentacarbonyl was also described recently during a synthesis of a modified pyrethroid [101]. 

Cu(l) and Fe(ll) complexes prepared in situ by reacting copper(l) or iron(ll) chloride with 1 equiv of ligand LI (tris(pyridin-2-ylmethyl)amine) or L2 are efficient catalysts for atom-transfer radical addition reactions. For instance, pent-4-enyl trichloroacetate was converted into 3,3,5-trichlorooxocan-2-one in 90% and 99% yield, respectively, when CuCl-Ll and CuCl-L2 were used as catalysts (Scheme 30) <2000J(P1)575>. 

Less suited for introduction of carbon No. 1 is the carbenoid from the Simmons-Smith-reaction of diiodoacetic-ester and zinc-copper [16], and the radical addition of chloroacetic ester using cuprous chloride and bipyridyl as a radical starter [17]. 

Martin P, Eginhard S, BeUus D. Copper(I)-catalyzed radical additions of polyhalogenated compounds to olefins. Part 1. Synthesis of polyhalogenated hutyryl chlorides, precursors of pyrethroid haloketenes. Helv. Chim. Acta 1980 63 (7) 1947-1957. 

Dehydrochlorination of 1,1,2-trichloroethane at 500°C in the presence of a copper catalyst gives a different product, ie, cis- and /n7 j -l,2-dichloroethylene. Addition of small amounts of a chlorinating agent, such as chlorine, promotes radical dehydrochlorination in the gas phase through a disproportionation mechanism that results in loss of hydrogen chloride and formation of a double bond. The dehydrochlorination of 1,2-dichloroethane in the presence of chlorine, as shown in equations 19 and 20, is a typical example. 

The copper-catalyzed 1 1 additions of aliphatic and aromatic sulfonyl chlorides or bromides to acetylenes yielding mixtures of trans- and cis-/ -halovinyl sulfones have also been described. Highly polar solvents favored trans addition, while cis addition predominated in low polarity media . A comparison between the thermal and the copper-catalyzed addition of sulfonyl bromides to phenylacetylene (cf. Scheme 6) enabled Amiel to suggest that the two stereoisomers do not have a common intermediate. That is, the trans addition product is a result of a normal radical chain, while the cis addition... 

The Meerwein arylation is at least formally related to the atom transfer method because a net introduction of an aromatic ring and a chlorine across a double bond is accomplished (Scheme 62). Facile elimination of HC1 provides an efficient route to the kinds of substituted styrenes that are frequently prepared by Heck arylations. Standard protocol calls for the generation of an arene diazonium chloride in situ, followed by addition of an alkene (often electron deficient because aryl radicals are nucleophilic) and a catalytic quantity of copper(II) chloride. It is usually suggested that the copper salt operates in a catalytic redox cycle, reducing the diazonium salt to the aryl radical as Cu1 and trapping the adduct radical as Cu11. 

At first it was thought that the copper methyl might react with the silicon halide in the manner of a Grignard reagent, but copper ethyl and copper phenyl prepared in ether suspension did not react with silicon tetrachloride. Neither did free methyl radicals from lead tetramethyl react with elementary, silicon, but they did add on silicon that was being chlorinated. This suggests that the third step in the mechanism is the addition of methyl groups to the chlorinated silicon formed in the cuprous chloride reduction ... 

Oxidation of C—bonds by copper ion catalyzed reaction with an organic peroxy ester (the Kha-rasch-Sosnovsky reaction) was at one time very popular for allylic oxidation and has been thoroughly reviewed. The reaction is usually carried out by dropwise addition of peroxy ester (conunonly r-butyl peracetate or r-butyl perbenzoate) to a stirred mixture of substrate and copper salt (0.1 mol % commonly copper(I) chloride or bromide) in an inert solvent at mildly elevated temperature (60-120 C). The mechanism involves three steps (i) generation of an alkoxy radical (ii) hyttogen atom abstractitm and (iii) radical oxidation and reaction with carboxylate anion (Scheme 11). 

Addition of catalytic or stoichiometric quantities of CuCN (TiCl)2 radically increases the reactivity of diorganozinc (R2Zn) and organozinc halide (RZnX) compounds. The resulting copper-zinc species (RCu(CN)ZnR or RCu(CN)ZnX) react with staimyl chlorides (RjSnCl) to give the corresponding alkylated stannyl derivatives (RjSnR)... 

Additional support for a free radical mechanism of the copper catalyzed reaction of red phosphorus with CH3CI or benzyl chloride comes from the isolation of methane, ethane, ethylene and propene in the CH3Cl-reaction and of trans stilbene and toluene in the PhCH2Cl-reaction, in addition to phosphonous dichlorides, RPCI2 (R = CH3, CgHjCHj ) 51) ... 

When saturated alkyl halides were used in place of allyl compounds, a zinc/cop-per couple or zinc dust/copper iodide promoted the 1,4-addition to a-enones or a-enals. Sonication enhanced the efficiency of the process leading to the 1,4-adducts in very good yields [166]. This reaction was later extended to various a,j3-unsaturated compounds such as esters, amides and nitriles [167]. The reactivity of the halide followed the order tertiary > secondary primary and iodide > bromide > chloride making the assumption of a radical process highly probable [168]. 

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