3638-35-5Relevant academic research and scientific papers
Clocking Tertiary Cyclopropylcarbinyl Radical Rearrangements
Engel, Paul S.,He, Shu-Lin,Banks,Ingold,Lusztyk
, p. 1210 - 1214 (2007/10/03)
Three independent methods have been employed to estimate the rate constant, k1, for ring-opening of the 2-cyclopropyl-2-propyl radical, 1, at room temperature. These three estimates are based on chemical trapping of 1 and the ring-opened 4-methylpent-3-ene-1-yl radical by thiophenol (k1 = (1.65 ± 0.41) × 107 M-1 s-1), 9-azabicyclo[3.3.1]nonane-N-oxyl (k1 = (1.76 ± 0.34) × 107 M-1 s-1) and 2,2,6,6-tetramethylpiperidine-N-oxyl (k1 = (2.1 ± 0.4) × 107 M-1 s-1) and absolute rate constants for nonrearranging radicals structurally related to 1. The mean value for k1) ((1.84 ± 0.4) × 107 M-1 s-1) should be used when 1 is employed as a tertiary alkyl free radical clock at ambient temperatures.
Hydrogen atom transfer reactions of transition-metal hydrides. Kinetics and mechanism of the hydrogenation of α-cyclopropylstyrene by metal carbonyl hydrides
Morris Bullock,Samsel, Edward G.
, p. 6886 - 6898 (2007/10/02)
The hydrogenation of α-cyclopropylstyrene (CPS) by a series of metal carbonyl hydrides (MH) gives a mixture of the unrearranged hydrogenation product Ph(CH3)(c-C3H5)CH (UN) and the rearranged hydrogenation product (E)-Ph(CH 3)C=CHCH2CH3 (RE). With the exception of HCr(CO)3Cp, second-order kinetics are found, conforming to the rate law -d[CPS]/dt = k[CPS][MH]. The proposed mechanism involves hydrogenation by sequential hydrogen atom transfers from the metal hydride to the organic substrate. The rate-determining step is the first hydrogen atom transfer in which a carbon-centered radical and a metal-centered radical are formed. In the case of HCr(CO)3Cp at 22 °C, the equilibrium constant for this step is K ～ 10-12. The effect of the significant amount of 17-electron *Cr(CO)3Cp radical formed in the hydrogenation of CPS by HCr(CO)3Cp is accommodated by the kinetic analysis. Since the initially formed carbon-centered radical undergoes first-order ring-opening rearrangement in competition with second-order trapping by MH, analysis of the product ratio as a function of [MH] concentration provides relative rates of hydrogen atom transfer from metal hydrides to a carbon-centered radical. Relative rates of hydrogen atom transfer at 60 °C from MH to 1 are as follows: krel = 1 for HMn(CO)4PPh3, krel = 4 for HMo(CO)3(C5Me5), krel = 93 for HMo(CO)3Cp, krel = 94 for HFe(CO)2(C5Me5). Comparison of the hydrogenation of CPS by HW(CO)3Cp and DW(CO)3Cp indicates that the kinetic isotope effect is inverse (kHW/kDW = 0.55) for the first hydrogen atom transfer but normal (kHW/kDW = 1.8-2.2) for the second hydrogen atom transfer. The first hydrogen atom transfer is endothermic, and its rate is largely influenced by the strength of the M-H bond. Steric effects appear to exert a dominant influence on the rate of the second hydrogen atom transfer, which is exothermic. Kinetic and mechanistic experiments indicate that hydrogenation of 2-cyclopropylpropene by HCr(CO)3Cp also occurs by a radical pathway.
HOMOALLYLIC SUBSTITUTION REACTIONS OF LITHIUM DIALKYL CUPRATES WITH CYCLOPROPYLCARBINYL HALIDES: MECHANISTIC CONSIDERATIONS
Hrubiec, Robert T.,Smith, Michael B.
, p. 1457 - 1468 (2007/10/02)
Highly reactive lithium dialkyl cuprates and 1-bromo-1-cyclopropylalkanes, 4, react to give good yields of the homoallylic substitution product, 6.Less reactive organocuprates react with 4 to give mixtures of 6 and the direct substitution product 7.These results are consistent with a copper(I) radical intermediate which undergoes facile rearrangement prior to reductive coupling.
