Quantum-Chemical Aspects of Diene-Phosphaalkene Cycloadditions

Penkovsky, Vladimir; Kharchenko, V. I.; Alexeiko, Leonid N.

doi:10.1080/10426509308045624

Cited by 7 publications

(1 citation statement)

References 5 publications

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“…The DA cycloadditions of phospha-1,3-butadienes with ethene were computed to be very exothermic with low activation energies . Ab initio investigations of the [2 + 4] cycloadditions of phosphaethene with 2 H -phosphole and with 1,3-butadiene − revealed such low activation energies and a preference for endo approach. It was concluded that the presence of phosphorus in a DA reactant lowers the activation energy relative to that of the hydrocarbon systems, due to the weakness of the CP π bond compared to the CC π bond .…”

Section: Introductionmentioning

confidence: 99%

Diels−Alder Reaction of Phosphaethene with 1,3-Dienes: An ab Initio Study

2002

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Computations on Diels-Alder (DA) reactions of phosphaethene with 1,3-butadiene and with isoprene reveal asynchronous transition structures. The DFT (B3LYP/6-311+G) activation energies of these reactions, 12-14 kcal/mol, are much lower than that of the parent ethene-butadiene reaction, 28 kcal/mol, even though the exothermicities of all lie in the same range, from -29 to -33 kcal/mol. The transition states (TSs) for the phosphethene-butadiene or isoprene DA reactions are earlier than the TSs of the butadiene-ethene cycloaddition. Due to the weakness of the C=P pi bond compared to the C=C pi bonds, the energies required to reach the phosphaethene TSs are much less than the carbocyclic cases. The computed (1)H NMR chemical shifts and nucleus independent chemical shifts (NICS) quantify the aromatic character of the transition states. Regioselectivities of the neutral phosphaethene-isoprene DA reactions are modest, at best. However, computations on radical cation DA reactions of phosphaethene with isoprene, which proceed stepwise with open chain intermediates, can account for the high regioselectivities that have been observed in some cases.

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