4325-49-9Relevant articles and documents
Solvolysis of 1,1-dimethyl-4-alkenyl chlorides: Evidence for π-participation
Malnar, Ivica,Juric, Sandra,Vrcek, Valerije,Gjuranovic, Zeljka,Mihalic, Zlatko,Kronja, Olga
, p. 1490 - 1495 (2002)
Tertiary 1,1-dimethyl-4-alkenyl chloride (1) solvolyzes with significantly reduced secondary β-deuterium kinetic isotope effect (substrate with two trideuteromethyl groups) and has a lower entropy and enthalpy of activation than the referent saturated analogue 4 (kH/kD = 1.30 ± 0.03 vs kH/kD = 1.79 ± 0.01; ΔΔH? = -9 kJ mol-1, ΔΔS? = -36 J mol-1 K-1, in 80% v/v aqueous ethanol), indicating participation of the double bond in the rate-determining step. Transition structure 1-TS computed at the MP2(fc)/6-31G(d) level of theory revealed that the reaction proceeds through a late transition state with considerably pronounced double bond participation and a substantially cleaved C-Cl bond. The doubly unsaturated compound 3 (1,1-dimethyl-4,8-alkadienyl chloride) solvolyzes with further reduction of the isotope effect, and a drastically lower entropy of activation (kH/kD = 1.14 ± 0.01; ΔS? = -152 ± 12 J mol-1 K-1, in 80% v/v aqueous ethanol), suggesting that the solvolysis of 3 proceeds by way of extended π-participation, i.e., the assistance of both double bonds in the rate-determining step.
On the mechanism of arene-catalyzed lithiation: The role of arene dianions - Naphthalene radical anion versus naphthalene dianion
Yus, Miguel,Herrera, Raquel P.,Guijarro, Albert
, p. 2574 - 2584 (2007/10/03)
The use of lithium and a catalytic amount of an arene is a well-established methodology for the preparation of organolithium reagents that manifest greater reactivity than the classical lithium-arene solutions. In order to rationalize this conduct, the participation of a highly reduced species, the dianion, is proposed and its reactivity explored. Studies of kinetics and of distribution of products reveal that the electron-transfer (ET) reactivity profile of dilithium naphthalenide in its reaction with organic chlorides excludes alternative mechanisms of halogen- lithium exchange. The process generates organolithium compounds. The dianion thus emerges along with the radical anion as a suitable candidate for catalytic cycles in certain processes. Endowed with a higher redox potential than its radical anion counterpart, dilithium naphthalene displays a broader spectrum of reactivity and so increases the range of substrates suitable for lithiation. The reaction of dilithium naphthalene with THF is one example of the divergent reactivity of the radical anion and the dianion, which has been the source of apparent misinterpretation of results in the past and has now been appropriately addressed.
Reactions of Saturated and Unsaturated Tertiary Alkyl Halides and Saturated Secondary Alkyl Iodides with Lithium Aluminum Deuteride. Convincing Evidence for a Single-Electron-Transfer Pathway
Ashby, E. C.,Welder, Catherine O.
, p. 7707 - 7714 (2007/10/03)
Reactions of saturated secondary and tertiary alkyl halides with LiAlH4 (LAH) and LiAlD4 (LAD) have been carried out, and convincing evidence for a single-electron-transfer (SET) pathway has been obtained. Reactions involving saturated alkyl halides with LAD provide a model system in which a halogen-atom radical chain process is not possible, and therefore, the observation of large quantities (in some cases >90 percent) of protium in the reduction product provides strong evidence for a radical intermediate and a SET pathway. Specifically, the reaction of 2-iodooctane (10) with LAD produced octane with a deuterium content as low as 21 percent. Also, the reaction of the tertiary halide 2-iodo-2-methylheptane (15) with LAD produced 2-methylheptane (16) with a deuterium content as low as 8 percent. The effect of stoichiometry, halogen type, and reaction vessel surface on these reactions was studied. Reaction of the unsaturated tertiary halide 6-iodo-6-methyl-1-heptene (25) with LAD was also studied and was found to proceed predominantly by a SET process involving a halogen-atom radical chain process. The possibility of a carbocation intermediate in all of these reactions is discussed.
Surface-mediated reactions. 3. Hydrohalogenation of alkenes
Kropp, Paul J.,Daus, Kimberlee A.,Tubergen, Mark W.,Kepler, Keith D.,Wilson, Vincent P.,Craig, Stephen L.,Baillargeon, Michelle M.,Breton, Gary W.
, p. 3071 - 3079 (2007/10/02)
Appropriately prepared silica gel and alumina have been found to mediate the addition of HCl, HBr, and HI to alkenes. The technique has been rendered even more convenient by the use of various organic and inorganic halides that undergo hydrolysis in the presence of silica gel or alumina to generate hydrogen halides in situ. Under these conditions alkenes such as cycloheptene (1), 1-octene (7), and 3,3-dimethyl-1-butene (15), which react with HCl only very slowly in solution, underwent rapid addition. 1-Octene (7) underwent ionic addition of HBr without competing radical addition. 1,2-Dimethylcyclohexane (24) afforded the syn addition product 25c, which underwent equilibration with the thermodynamically more stable isomer 25t. A mechanism for surface-mediated addition/elimination is proposed involving a stepwise transfer of H+ and X- from or to the surface in syn fashion, as shown in Scheme II.
