- Photochemical 1,3-stannyl rearrangement of allylic stannanes
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The photochemical 1,3-stannyl rearrangement of allylic stannanes has been investigated. The photorearrangement of (E)-cinnamyl(triphenyl)stannane is not observed in benzene under anaerobic conditions, while the photoinduced 1,3-stannyl migration takes place in the same solvent under aerobic conditions, or in the presence of organic halides or a radical-trapping agent to give a photoequllibrium mixture of the cinnamylstannane and its branched regioisomer, 1-phenylprop-2-enyl(triphenyl)stannane, with the latter predominating. Cinnamyl(trialkyl)stannanes and their homologues also afford the corresponding branched allylstannanes under similar photochemical conditions. These 1,3-stannyl migrations proceed intramolecularly via cinnamyl π-π* excitation in competition with homolytic (cinnamyl)C-Sn bond fission. In contrast, the 1,3-stannyl migration of crotyl- and prenyl-(tributyl)-stannanes is not efficient, but their triphenyl or dibutylphenyl derivatives undergo the 1,3-rearrangement via excitation of the phenyl group(s) on the tin atom to give a regioisomeric mixture of the starting linear tin compounds and the branched ones with the former predominating.
- Takuwa, Akio,Kanaue, Takashi,Yamashita, Koichi,Nishigaichi, Yutaka
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p. 1309 - 1314
(2007/10/03)
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- Wurtz-type reductive coupling reaction of allyl bromides and haloorganotins in cosolvent/H2O(NH4Cl)/Zn media as a route to allylstannanes and hexaaryldistannanes
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Twenty-one allylstannanes have been prepared via a simple Wurtz-type coupling reaction of allyl bromides and R3SnX compounds (R = Me, Et, Pr, Bu, Ph; X = Cl, I, OH), Bu2SnCl2, and (Bu2SnCl)2O in cosolvent/H2O (NH4Cl saturated) media under the mediation of zinc powder. Also R3SnSnR3 compounds (R = Ph, p- and m-Tol) have been prepared via coupling of triaryltin chlorides. The stereochemical course of the reaction between R3SnCl and (C4H7)Br (C4H7 = α-methylallyl, trans- and cis-crotyl) has been extensively studied. Two distinct reactions are involved in the overall process: (i) the coupling reaction, which gives rise stereoselectively to the sole R3SnCH(CH3)CH=CH2 (α-isomer), and (ii) the subsequent isomerization of the α-isomer furnishing mixtures of (α, trans, cis)-isomers. The occurrence of reaction ii depends upon the nature either of the R group or the employed cosolvent. In cyclohexane, the α-isomer is exclusively obtained with R = Bu, while with R = Me, Et, and Pr it is found as a major component in the ternary isomeric mixture. In tetrahydrofuran, 2-propanol, acetonitrile, and pyridine, the isomerization occurs to an extent which depends on the polarity and the coordinating ability of the cosolvent itself. The observed stereoselection has been hypothesized to occur through one-electron transfer from the zinc metal to the (C4H7)Br to form stereoselectively an adsorbed CH2=CHCH(CH3)Br?-Zn?+ radical ion which is trapped by the R3SnCl reactant to form the α-isomer. Similarly, ditin compounds are thought to be formed by interaction of R3SnCl?-Zn?+ radical ions with R3SnCl molecules.
- Von Gyldenfeldt, Friederike,Marton, Daniele,Tagliavini, Giuseppe
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p. 906 - 913
(2008/10/08)
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- Radical Reactions in Synthesis: Carbon-Carbon Bond Formation from 2-Substituted Allyl Trialkyl Stannanes
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A competing 1,3-rearrangement of allyl stannanes has been demonstrated to occur under the normal thermal homolytic allyl transfer reaction conditions which limits the substitution patterns in these processes; two methacrylyl stannanes are described which allow the transfer of the methacrylyl moiety to alkyl bromides and iodides under mild conditions.
- Baldwin, Jack E.,Adlington, Robert M.,Birch, David J.,Crawford, James A.,Sweeney, Joseph B.
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p. 1339 - 1340
(2007/10/02)
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