- Substitution Reactions in the β-Styryl and Phenylethynyl Systems
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Substitution for Q in the systems PhCH=CHQ, Ph2C=CHQ, and PhCCQ can occur by a free-radical chain mechanism where the attacking radical is alkyl (Q = HgX, Bu3Sn, PhSO2, PhSO, PhS, Cl, Br, I) or (EtO)2PO. (Q = HgX, Bu3Sn, I).The Q. radicals formed by β-elimination can generate t-Bu. or (EtO)2PO. by reaction with t-BuHgCl, Hg2, ClHg or by electron transfer between .HgCl and (EtO)2PO-.With Q = PhS or PhSO2, relative reactivity data indicates that the free radical addition-elimination sequence occurs for t-BuLi at 0 or 45 deg C andthat this process may also be involved in reactions of t-BuMgCl or tert-butyl cuprates with some of the substrates.Ionic reaction of (EtO)2PO- with the three substrates with Q = PhSO2 or halogen are examined.With Q = PhSO2, PhCHCH2P(O)(OEt)2, Ph2C=CHP(O)(OEt)2, and PhCCP(O)(OEt)2 are formed in good yield.
- Russell, Glen A.,Ngoviwatchai, Preecha
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p. 1836 - 1842
(2007/10/02)
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- Reactions of Alkylmercurials with Heteroatom-Centered Acceptor Radicals
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The relative reactivities of alkylmercury halides toward PhS., PhSe., or I. decrease drastically from R = tert-butyl to R = sec-alkyl to R = n-butyl, indicative that R. is formed in the rate-determining step in the attack of these radicals upon RHgCl.The alkyl radicals thus formed will enter into chain reactions in which a heteroatom-centered radical (A.) is regenerated from substrates such as RS-SR, ArSe-SeAr, ArTe-TeAr, PhSe-SO2Ar, Cl-SO2Ph; ZCH=CHA (A = Cl, I, SPh, SO2Ph); or PhCCHA (A = I, SPh, SO2Ph). β-Styrenyl (PhCH=CHA, Ph2C=CHA) and β-phenethynyl (PhCCA) systems with A = I, Br, SO2Ph also enter into chain reactions with mercury(II) salts with the ligands PhS, PhSe, PhSO2, or (EtO)2PO.The relative reactivities of a series of reagents toward t-Bu. and of PhCH=CHA, Ph2C=CHA, and PhCCA toward c-C6H11. are reported as well as the regioselectivity of t-Bu. attack observed for 1,2-disubstituted ethylenes (ZCH=CHA) with Z and A from the group Ph, Cl, Br, I, SO2Ph, SPh, Bu3Sn.Reactions of (E)- and (Z)-PhCH=CHI or MeO2CCH=CHI with t-Bu. or c-C6H11. occurred in a regioselective and stereospecific (retention) manner.Reactions of (E)- and (Z)-ClCH=CHCl occurred in a nonstereospecific manner in which the E/Z product ratio increased with the bulk of the attacking radical.A similar effect on the E/Z product ratios was observed for (Z)-MeO2CCH=CHCl.
- Russell, Glen A.,Ngoviwatchai, Preecha,Tashtoush, Hasan I.,Pla-Dalmau, Anna,Khanna, Rajive K.
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p. 3530 - 3538
(2007/10/02)
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