123499-10-5Relevant articles and documents
Mechanism of the diphenyldisulfone-catalyzed isomerization of alkenes. Origin of the chemoselectivity: Experimental and quantum chemistry studies
Markovic, Dean,Varela-Alvarez, Adrian,Sordo, Jose Angel,Vogel, Pierre
, p. 7782 - 7795 (2006)
Polysulfone- and diphenyldisulfone-catalyzed alkene isomerizations are much faster for 2-alkyl-1-alkenes than for linear, terminal alkenes. The mechanism of these reactions has been investigated experimentally for the isomerization of methylidenecyclopentane into 1-methylcyclopentene, and theoretically [CCSD(T)/6-311++G(d,p)//B3LYP/6-311++G(d,p) calculations] for the reactions of propene and 2-methylpropene with a methanesulfonyl radical, MeSO 2?. On heating, polysulfones and (PhSO2)2 equilibrate with sulfonyl radicals, RSO2?. The latter abstract allylic hydrogen atoms in one-step processes giving allylic radical/RSO 2H pairs that recombine within the solvent cage producing the corresponding isomerized alkene and RSO2?. The sulfinic acid, RSO2H, can diffuse out from the solvent cage (H/D exchange with MeOD,D2O) and reduce an allyl radical. Calculations did not support other possible mechanisms such as hydrogen exchange between alkenes, electron transfer, or addition/elimination process. Kinetic deuterium isotopic effects measured for the (PhSO2)2-catalyzed isomerization of methylidenecyclopentane and deuterated analogues and calculated for the H abstraction from 2-methylpropene and deuterated analogues by CH 3-SO2? are consistent also with the one-step hydrogen transfer mechanism. The high chemoselectivity for this reaction is not governed by an exothermicity difference but by a difference in ionization energies of the alkenes. Calculations for CH3SO2? + propene and CH3SO2? + 2-methylpropene show a charge transfer of 0.34 and 0.38 electron, respectively, from the alkenes to the sulfonyl radical in the transition states of these hydrogen abstractions.
Transition-State Structure Variation in the Diels-Alder Reaction from Secondary Deuterium Kinetic Isotope Effects: The Reaction of Nearly Symmetrical Dienes and Dienophiles Is Nearly Synchronous
Gajewski, Joseph J.,Peterson, Karen B.,Kagel, John R.,Huang, Y. C. Jason
, p. 9078 - 9081 (1989)
Secondary deuterium kinetic isotope effects (KIEs) in the reaction of acrylonitrile, fumaronitrile, vinylidene cyanide, dimethyl fumarate and maleate, and methyl trans-β-cyanoacrylate with isoprene were determined by competition with isoprene-d0 (d0), 4,4-dideuterioisoprene (4,4-d2), and 1,1,4,4-tetradeuterioisoprene (d4).The d4 experiment gives the KIE for 1,1-dideuterioisoprene from the KIEs for 4,4-d2.The KIEs for bond making to the β site of acrylonitrile and vinylidene cyanide are much more inverse than those at the α bond making site but are less than the maximum value expected, which indicates an early, unsymmetrical, concerted transition state.The effects wit fumaronitrile are the same for both 1,1- and 4,4-dideuterioisoprene, indicating equivalent effects at both sites and not bonding to the preferred C-1 site of isoprene most of the time.The KIEs with methyl trans-β-cyanoacrylate are inverse at both bond-making sites to the dienophile and both nearly one-third of the maximum value expected.The results with nearly symmetrical addends are not consistent with a two-step reaction, particularly one with the second step being rate determining, or with a concerted reaction with a highly unsymmetrical transition state, but rather with a concerted pathway that is nearly synchronous.The KIEs with methyl fumarate and maleate suggest an unsymmetrical transition state, but they are within experimental error of a symmetrical transition state.
