6319-18-2Relevant articles and documents
Dimerization and Cycloaddition Reactions of a Trimethylenemethane Derivative, 2-Isopropylidenecyclopenta-1,3-diyl. Mechanistic Separation of Triplet and Singlet Reactions
Corwin, Leonard R.,McDaniel, Dale M.,Bushby, Richard J.,Berson, Jerome A.
, p. 276 - 287 (1980)
Pyrolysis of 7-isopropylidene-2,3-diazanorbornene (1) at 60 deg C in solution liberates N2 and 2-isopropylidenecyclopenta-1,3-diyl (2).The diyl (2) dimerizes readily, but, in the presence of an olefinic trapping agent, 2 can be intercepted as either a fused adduct, F, a bicyclooct-1-ene, or a bridged adduct, B, a 7-isopropylidenenorbornane.The composition of the adduct mixture is dependent on the initial concentration of the trapping olefin, fused adducts being heavily favored at high concentrations.The concentration dependence arises from two forms of the diyl which are generated sequentially in a cascade mechanism.The first species is a singlet that can add both regiospecifically and stereospecifically, whereas the second is the triplet ground state of the diyl.Quantitative treatment of the dilution effect data for the addition of dimethyl fumarate leads to the conclusion that the rate constants for capture of the singlet and intersystem crossing to the triplet are in the ratio 7.7 M-1.
A Ranking of Diylophilic Reactivities of Olefins toward the Singlet and Triplet Forms of the Trimethylenemethane Biradical, 2-Isopropylidenecyclopenta-1,3-diyl
Duncan, Charles D.,Corwin, Leonard R.,Davis, James H.,Berson, Jerome A.
, p. 2350 - 2358 (2007/10/02)
The relative rates of cycloaddition of olefins with the trimethylenemethane (TMM) derivative 2-isopropylidenecyclopenta-1,3-diyl (1) can be determined by direct competition experiments.The gross relative activities in turn can be dissected into singlet and triplet relative reactivities by two techniques.The first involves the determination of the competition ratio for entrapment of the singlet TMM by a given olefin vs. intersystem crossing (isc) to the triplet, combined with the assumption that the rate of isc is independent of the olefin.The second uses the concentration of a "marker" product from the limiting singlet product distribution (obtained from oxygen-saturated runs) and the limiting spin-equilibrated (mostly triplet) product distribution as a guide to the fraction of singlet-derived and triplet-derived products from a given olefin under the conditions of competition.The relative reactivities toward the singlet follow: maleic anhydride, 235; maleonitrile, 180; fumaronitrile, 160; dimethyl fumarate, 67; acrylonitrile, 4.5; methyl acrylate, 0.9; dimethyl maleate, 1.0.The relative triplet reactivities for the last four olefins are respectively 59, 35, 12, and (1.0).The results are consistent with the idea of a concerted cycloaddition of the singlet and a nonconcerted one of the triplet.
