- Selective Cross Coupling via Oxovanadium(V)-Induced Oxidative Desilylation of Benzylic Silanes
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Benzylic silanes bearing an electron-donating group at the ortho- or para-position underwent the oxovanadium(V)-induced one-electron oxidative desilylation due to low ionization potential, which was applied to the intermolecular regioselective coupling with allylic silanes or silyl enol ether.
- Hirao, Toshikazu,Fujii, Takashi,Ohshiro, Yoshiki
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p. 8005 - 8008
(2007/10/02)
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- Photochemistry of phosphate esters: An efficient method for the generation of electrophiles
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The photochemical cleavage of benzyl diethyl phosphates, 1a-g, has been examined in tert-butyl alcohol, which produces the corresponding benzyl tert-butyl ether as the major solvolysis product upon direct irradiation. The multiplicity of the reactive excited state has been established as the singlet state. Evidence favoring an intermediate benzyl cation-phosphate ion pair formed from photofragmentation includes oxygen-18 scrambling, racemization of chiral benzyl phosphates, and substituent effects on the rate of reaction. The existence of an electrophilic intermediate is further supported by a linear free energy relationship for the rate of disappearance of 1, kdis, with Hammett σ, which gave a ρ value of -0.90 and for the rate of appearance of 2, kapp, a Hammett ρ value of -0.97. Possible mechanisms including an electron transfer either before or after homolysis or simple heterolysis of the ester bond are evaluated.
- Givens, Richard S.,Matuszewski, Bogdan,Athey, Phillip S.,Robert Stoner
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p. 6016 - 6021
(2007/10/02)
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- Regioselective Ring Opening in Substituted Benzocyclopropenes. An Alternative or Complementary Mechanism for Electrophilic Substitution Involving Attack at a ? Bond
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2-Methylbenzocyclopropene (5) reacts with bromine, iodine, and HCl to give the m-xylenes 12a,c,d as the major products, whereas it reacts with silver nitrate in the presence of ethanol and aniline to give the o-xylenes 11e,f as the major products.Similarly, 3-methylbenzocyclopropene (10) gives mainly m-xylenes 14a,c,d with halogens and HCl and gives p-xylenes 13e,f with silver nitrate and ethanol or aniline.Cyclopropabenzocyclobutene (15) also gives different products with halogens and silver nitrate, but in this case HCl gives the same type of product as the silver ion.The difference in electrophilic behavior of 5, 10, and 15 toward the two types of reagents is suggested to arise from attack of the silver ion (and the proton in the case of 15) on the ? electrons of the cyclopropyl ring.
- Bee, Lim Keow,Garratt, Peter J.,Mansuri, Muzamil M.
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p. 7076 - 7079
(2007/10/02)
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