- Divergent C-H Oxidative Radical Functionalization of Olefins to Install Tertiary Alkyl Motifs Enabled by Copper Catalysis
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An efficient tertiary alkylation reaction of olefins with 1,3-dicarbonyl compounds was developed by virtue of copper catalyst without the use of expensive ligands or additives. In contrast to alkyl Heck-type reaction, alkyl halide is not required. Notably
- Tian, Ming-Qing,Wang, Cong,Hu, Xu-Hong,Loh, Teck-Peng
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- Carbon-carbon bond formation by radical addition-fragmentation reactions of O-alkylated enols
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α-tert-Butoxystyrene [H2C = C(OBut)Ph] reacts with α-bromocarbonyl or α-bromosulfonyl compounds [R 1R2C(Br)EWG; EWG = -C(O)X or -S(O2)X] to bring about replacement of the bromine atom by the phenacyl group and give R 1R2C(EWG)CH2C(O)Ph. These reactions take place in refluxing benzene or cyclohexane with dilauroyl peroxide or azobis(isobutyronitrile) as initiator and proceed by a radical-chain mechanism that involves addition of the relatively electrophilic radical R 1R2(EWG)C* to the styrene. This is followed by β-scission of the derived α-tert-butoxybenzylic adduct radical to give But*, which then abstracts bromine from the organic halide to complete the chain. α-1-Adamantoxystyrene reacts similarly with R 1R2C(Br)EWG, at higher temperature in refluxing octane using dα-tert-amyl peroxide as initiator, and gives phenacylation products in generally higher yields than are obtained using α-tert-butoxystyrene. Simple iodoalkanes, which afford relatively nucleophilic alkyl radicals, can also be successfully phenacylated using α-1-adamantoxystyrene. O-Alkyl O-(tert-butyldimethylsilyl) ketene acetals H2C=C(OR)OTBS, in which R is a secondary or tertiary alkyl group, react in an analogous fashion with organic halides of the type R1R2C(Br)EWG to give the carboxymethylation products R1R2C(EWG)CH 2CO2Me, after conversion of the first-formed silyl ester to the corresponding methyl ester. The silyl ketene acetals also undergo radical-chain reactions with electron-poor alkenes to bring about alkylation-carboxymethylation of the latter. For example, phenyl vinyl sulfone reacts with H2C=C(OBut)OTBS to afford Bu tCH2CH(SO2Ph)CH2CO2Me via an initial silyl ester. In a more complex chain reaction, involving rapid ring opening of the cyclopropyldimethylcarbinyl radical, the ketene acetal H 2C=C(OCMe2C3H5-cyclo)OTBS reacts with two molecules of N-methyl- or N-phenyl-maleimide to bring about [3 + 2] annulation of one molecule of the maleimide, and then to link the bicyclic moiety thus formed to the second molecule of the maleimide via an alkylation-carboxymethylation reaction.
- Cai, Yudong,Roberts, Brian P.,Tocher, Derek A.,Barnett, Sarah A.
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p. 2517 - 2529
(2007/10/03)
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- Carbon-carbon bond formation by radical addition-fragmentation reactions of O-tert-alkyl enols and O-cyclopropylcarbinyl enols
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Terminal alkenes of the type H2C=C(OR1)X, in which R1 is a tertiary alkyl or a 1-cyclopropylethyl group and X=Ph, OSiMe2But, OEt or H, undergo radical-chain reactions with organic halides R2Hal to give carbonyl compounds R2CH2C(=O)X.
- Cai, Yudong,Roberts, Brian P.
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p. 4645 - 4648
(2007/10/03)
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- Radical and Ionic Reactions of (Benzoylmethyl)mercurials
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Photolysis of PhCOCH2HgCl or (PhCOCH2)2Hg yields benzoylmethyl radicals which can be trapped by anions such as Me2C=NO2-, RC(CO2Et)2-, RC(O-)=CH2 or by other electron-rich systems such as (RO)3P, N-methylpyrrole, enamines, or norbornene.Electron transfer from the adduct radicals to the mercurials yields PhCOCH2A from the anions A-, PhCOCH2P(O)(OR)2 from P(OR)3, and the phenacyl derivative from N-methylpyrrole or enamines.Easily oxidized anions such as PhCOCPh2- or PhC(CH3)=NO2- react with PhCOCH2* by electron transfer to yield the dimer derived from the anion.Addition of PhCOCH2* to norbornene yields a substituted 3-benzoylpropyl radical which cyclizes at the ortho position of the benzoyl group to give the α-tetralone derivative.
- Russell, Glen A.,Kulkarni, Shekhar V.,Khanna, Rajive K.
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p. 1080 - 1086
(2007/10/02)
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