Atom transfer radical additions acetate

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

Controlled/ Living radical polymerization (CRP) of vinyl acetate (VAc) via nitroxide-mediated polymerization (NMP), organocobalt-mediated polymerization, iodine degenerative transfer polymerization (DT), reversible radical addition-fragmentation chain transfer polymerization (RAFT), and atom transfer radical polymerization (ATRP) is summarized and compared with the ATRP of VAc catalyzed by copper halide/2,2 6 ,2 -terpyridine. The new copper catalyst provides the first example of ATRP of VAc with clear mechanism and the facile synthesis of poly(vinyl acetate) and its block copolymers. 

AA sec acrylic acid abstraction sec hydrogen atom transfer abstraction v,v addition and micleophilicity 35 by aikoxy radicals 34-5, 124-5, 392 by alkoxycarbonyloxy radicals 103,127-8 by alkyl radicals 34 5, 113, 116 by f-amyloxy radicals 124 by arenethiyl radicals 132 by aryl radicals 35, 118 by benzovloxy radicals 35, 53, 120, 126 wilh MM a" 53, 120 by /-butovy radicals 35, 53, 55, 124 solvent effects 54, 55. 123 with alkenes 122 3 with ally I acrylates 122 wilh AMS 120, 123 wilh BMA 53, 123 with isopropenvl acetate 121 with MA 120 with MAN 121 with MMA 53, 55, 120.419 with VAc 121 with vinyl ethers 123... 

All the examples presented under Sect. 4.1 used an iodine atom transfer to generate the desired radicals. Another approach involving abstraction of hydrogen atom is also reported. For instance, ethers and acetals undergo direct intermolecular addition to aldehydes under treatment with Et3B/air... 

A limitation of the aforementioned methods is that they are unsuitable for the use of primary alkyl iodides. Under Et3B/02 initiation conditions, the desired radical is intended to be generated by iodine atom transfer to ethyl radicals, which is not favorable in the case of primary iodides. Thus ethyl radical addition competes with the desired radical when using triethylborane initiation along with primary iodides. In addition, generating radicals by hydrogen atom transfer from ethers or acetals has limited applicability. Because of the expanded synthetic potential of primary alkyl iodides as... 

Reaction sequences involving halogen transfer, followed by non-radical interception of the alkyl iodide or bromide formed can allow for the trapping of products arising from less exothermic or even endothermic atom transfer additions and are exemplified in Scheme 11. Yoon [30] and Curran [31] have demonstrated that the a-halo ethers formed upon addition to vinyl ethers can be trapped with alcohols, leading to formation of acetals. Substitution reactions on the heteroaromatics pyrrole and indole have been carried out through a sequence of steps involving I- or Br-... 

When such comparisons are made it becomes clear that the reactivities of radicals, monomers, or transfer agents depend on the particular reaction being considered. It is not possible to conclude, for example, that polyfvinyl acetate) radical will always react x times more rapidly than polystyrene radical in addition reactions or y times as rapidly in the atom abstraction reactions involved in chain transfer. Similarly the relative order of efficiency of chain transfer agents will not be the same for all radical polymerizations. This is because resonance, sleric, and polar influences all come into play and their effects can depend on the particular species involved in a reaction. 

Electron transfer from Me2C=C(OMe)OSiMe3 to Q is made possible by the strong interaction between Q" and Mg + (or 2Mg +) to produce the radical ion pair. Since the spin of the ketene silyl acetal radical cation is mainly localized on the terminal carbon atom [229], the carbon -oxygen bond is formed before the cleavage of the Si-0 bond to yield the adduct (Scheme 15). This contrasts with the 1,2-addition of nonsubstituted ketene silyl acetal [H2C=C(OEt)OSiEt3] via nucleophilic attack to the positively charged carbonyl carbon of the quinone rather than via an alternative electron transfer pathway [228]. 

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