Addition atom transfer radical

The addition of halocarbons (RX) across alkene double bonds in a radical chain process, the Kharasch reaction (Scheme 9.29),261 has been known to organic chemistry since 1932. The overall process can be catalyzed by transition metal complexes (Mt"-X) it is then called Atom Transfer Radical Addition (ATRA) (Scheme 9.30).262... 

Scheme 9.30 Atom Transfer Radical Addition (ATRA)...

Novel catalytic systems, initially used for atom transfer radical additions in organic chemistry, have been employed in polymer science and referred to as atom transfer radical polymerization, ATRP [62-65]. Among the different systems developed, two have been widely used. The first involves the use of ruthenium catalysts [e.g. RuCl2(PPh3)2] in the presence of CC14 as the initiator and aluminum alkoxides as the activators. The second employs the catalytic system CuX/bpy (X = halogen) in the presence of alkyl halides as the initiators. Bpy is a 4,4/-dialkyl-substituted bipyridine, which acts as the catalyst s ligand. 

Transition metal-catalyzed atom transfer radical addition Atom transfer radical polymerization Equilibrium constant for atom transfer Activation rate constant for atom transfer Deactivation rate constant for atom transfer 2,2 -Bipyridine... 

Carbon-carbon bond formation is a fundamental reaction in organic synthesis [1, 2,3,4], One way to form such a bond and, thus, extend a carbon chain is by the addition of a polyhalogenated alkane to an alkene to form a 1 1 adduct, as shown in Scheme 1. This reaction was first reported in the 1940s and today is known as the Kharasch addition or atom transfer radical addition (ATRA) [5,6], Historically, Kharasch addition reactions were conducted in the presence of radical initiators or... 

Another application of ruthenium indenylidene complexes was the atom transfer radical addition of carbon tetrachloride to vinyl monomers reported by Verpoort [61]. This Kharasch reaction afforded good yields for all substrates tested, especially with the catalyst VIII (Equation 8.11, Table 8.8). 

Kleij, A.W., Gossage, R.A., Gebbink, R.J.M.K., Brinkmann, N., Reijerse, E.J., Kragl, U., Lutz, M., Spek, A.L. and van Koten, G. (2000) A dendritic effect in homogeneous catalysis with carbosilane-supported arylnickel(II) catalysts observation of active-site proximity effects in atom-transfer radical addition. J. Am. Chem. Soc., 122, 12, 112. 

Fiirstner reported the first McMurry-type reactions working with 5-10 mol% of titanium trichloride and stoichiometric amounts of zinc powder in the presence of chlorotrimethylsilane. The amount of TiCl3 could be reduced to 2 mol% when (ClMe2SiCH2)2 was used as a reagent [125, 131]. At the same time, Burton and coworkers reported atom transfer radical additions of perfluoroalkyl iodides 39 to alkenes 40 catalyzed by 20 mol% of a low-valent titanium compound generated from TiCLt and zinc powder affording 41 in 10-85% yield (Fig. 13). A tandem radical addition/5-exo cyclization/iodine transfer reaction with diallyl ether proceeded in 66% yield [132]. 

Fig. 13 Low-valent titanium-catalyzed atom transfer radical additions...

Fig. 37 Atom transfer radical addition reactions catalyzed by molybdenum complexes...

Fig. 43 Atom transfer radical addition/cyclizations initiated by Mn2(CO)10...

Nedelec and coworkers reported a manganese(III)-initiated cyanoacetate-catalyzed atom-transfer radical addition of polyhalomethanes or dibromomalonate 172 to alkenes 126 (Fig. 48) [272]. Since neither Mn(II) nor Mn(III) is useful to initiate Kharasch-type additions, an organocatalyst served this purpose. Thus, a short electrolysis of a mixture of 126,172,10 mol% of Mn(OAc)2, and 10 mol% of methyl cyanoacetate 171 led to initial oxidation of Mn(II) to Mn(III), which served to form the cyanoacetate radical 171A oxidatively. The latter is able to abstract a halogen atom from 172. The generated radical 172A adds to 126. The secondary... 

Ivzed atom transfer radical additions Fig. 48 Manganese(IH) acetate-cataiyz... 

Brace reported atom transfer radical addition/cyclization sequences of 1,6-dienes 50 with CC14 using 1 mol% FeCl3 as the catalyst and benzoin as the reducing... 

Cu(0)-Catalyzed Atom Transfer Radical Addition Reactions. 384... 

Fig. 36 Pd(0)-catalyzed atom transfer radical addition reactions...

Electron transfer from copper or copper salts to alkyl halides has been used to initiate atom transfer radical additions. One modification of this process involves catalytic amounts of copper powder and fluorinated alkyl iodides the radicals so generated may react in either inter- or intramolecular fashion with alkenes (equation 13)19. Alternatively, a-chloroesters with remote alkene functions undergo cyclization in the presence of cat-... 

Complexes RuCl2(PCy3)(L)(=C=CHt-Bu) (L) are also good precursors for the Karasch reaction they catalyse the atom-transfer radical addition of CC14 and CHC13 to various olefins such as acrylates,styrene and 1-octene [78]. 

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>. 

This catalytic sequence is known as Kharasch addition or atom transfer radical addition (ATRA) [4]. Various polyhalogenated compounds such as CCI4 and CCI3CO2R are used as the organic halides, and transition metal salts or complexes are used as the catalyst [3]. Intramolecular version of the Kharasch addition reaction (atom transfer radical cyclization, ATRC) has opened novel synthetic protocols to the synthesis of carbocyde or heterocyles catalyzed by transition metals [5-7], and this has become a very important field in free radical cydization in organic synthesis. Transition metal-catalyzed Kharasch reactions sometimes afford telomers or poly-... 

---