Computational Explorations of Vinylcyclopropane−Cyclopentene Rearrangements and Competing Diradical Stereoisomerizations

Nendel, Maja; Sperling, Dirk; Wiest, Olaf; Houk, K. N.

doi:10.1021/jo991026f

Cited by 53 publications

(41 citation statements)

References 41 publications

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“…Both studies agree on the biradical nature of the rearrangement and on the preference for the si-stereochemistry of rearrangement suggested by the WoodwardÀHoffmann rules [3]. For the unsubstituted system, two more TSs, slightly (0.3 -1.1 kcal mol À1 ) higher in energy, were calculated; they were reached by motions deviating from the minimal-energy pathway [9]. These results suggest that dynamical calculations might be more suited for the description of the vinylcyclopropane !…”

supporting

confidence: 78%

The Rearrangement of 2,2‐Diphenyl‐1‐[(E)‐2‐phenylethenyl]cyclopropane to 3,4,4‐Triphenylcyclopent‐1‐ene: a DFT Analysis

Sicking

Sustmann

Mulzer

et al. 2011

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Dedicated to Paul von Ragué Schleyer, friend and mentor, on the occasion of his 80th birthday A computational study on the rearrangement of 2,2-diphenyl-1-[(E)-2-phenylethenyl]cyclopropane (1) is presented, using density functional theory (DFT), (U)B3LYP with the 6-31G* basis set (DFT1) and (U)M05-2X with the 6-311 þ G** basis set (DFT2). In agreement with a biradical character of the transition structure (TS) or intermediate, the potential-energy hypersurface is lowered by the influence of three conjugated Ph groups. Surprisingly, two conformations of the geminal diphenyl group (different twist angles) induce two different minimum-energy pathways for the rearrangement. Independent of the functional used, the first hypersurface harbors true biradical intermediates, whereas the second energy surface is a flat, slightly ascending slope from the starting material to the TS. The functional (U)M05-2X with the basis set 6-311 þ G** provides realistic energies which seem to be close to experiment. The activation energy for racemization of enantiomers of 1 is lower than that of rearrangement by 2.5 kcal mol À1, in agreement with experiment.1. Introduction. -The rearrangement of vinylcyclopropane and its derivatives to substituted cyclopentenes has played an important role in the development of mechanistic and theoretical organic chemistry. Ever since the discovery of this reaction, independently by Vogel [1], and by Overberger and Borchert [2], it has been studied experimentally and theoretically. It played a role in the presentation of the WoodwardÀHoffmann rules [3], was recognized early as involving biradical intermediates [3 -5], and was analyzed by quantum-chemical calculations [6] [7]. A critical review on mechanistic aspects of this rearrangement was provided by Baldwin [8].The reaction exhibits both aspects, that of a concerted and a stepwise mechanism. However, calculations on the potential-energy surface of the unsubstituted system display only one transition structure (TS) for rearrangement and no intermediate [6]. The potential-energy surface is rather flat and diradical in nature. The TS is a biradical which undergoes ring closure to cyclopentene. The results of Houks group closely resemble those of Davidson and Gajewski [7], who took a slightly different approach. Both studies agree on the biradical nature of the rearrangement and on the preference for the si-stereochemistry of rearrangement suggested by the WoodwardÀHoffmann rules [3]. For the unsubstituted system, two more TSs, slightly (0.3 -1.1 kcal mol À1 )

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confidence: 78%

The Rearrangement of 2,2‐Diphenyl‐1‐[(E)‐2‐phenylethenyl]cyclopropane to 3,4,4‐Triphenylcyclopent‐1‐ene: a DFT Analysis

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Mulzer

et al. 2011

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“…In 1997, Houk et al [15], as well as Davidson and Gajewski [16], reported on calculations of the vinylcyclopropane rearrangement by UB3LYP/6-31G*, confirmed by CAS-SCF(4,4) studies. A later extended version by Houk and co-workers included calculations of 2'-(tert-butyl)-and several methylated vinylcyclopropanes [17].…”

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confidence: 99%

“…Structures on this plane return to s-gauche-2 without a barrier. The mentioned TS is essentially pure diradical in character [17] and corresponds to the endo-allylic 3 in Scheme 1. Yet, the reaction is concerted, and the TS is located on the si pathway.…”

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confidence: 99%

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1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Mulzer

Huisgen

Arion

et al. 2011

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Dedicated to Paul von Ragué Schleyer, friend and mentor, on the occasion of his 80th birthday Kinetic measurements for the thermal rearrangement of 2,2-diphenyl-1-[(E)-styryl]cyclopropane (22a) to 3,4,4-triphenylcyclopent-1-ene (23a) in decalin furnished DH = isom ¼ 31.0 AE 1.2 kcal mol À1 and DS = isom ¼ À 6.0 AE 2.6 e.u. The lowering of DH = by 20 kcal mol À1, compared with the rearrangement of the vinylcyclopropane parent, is ascribed to the stabilization of a transition structure (TS) with allylic diradical character. The racemization of (þ)-(S)-22a proceeds with DH = rac ¼ 28.2 AE 0.8 kcal mol À1and DS = rac ¼ À 5 AE 2 e.u., and is at 1508 106 times faster than the rearrangement. Seven further 1-(2-arylethenyl)-2,2-diphenylcyclopropanes 22, (E)-and (Z)-isomers, were synthesized and characterized. The (E)-compounds showed only modest substituent influence in their k rac (at 119.48) and k isom (at 159.38) values. The lack of solvent dependence of rate opposes charge separation in the TS, but a linear relation of log k rac with log p.r.f., i.e., partial rate factors of radical phenylations of ArH, agrees with a diradical TS. The ring-opening of the preponderant s-trans-conformation of 22 gives rise to the 1-exophenylallyl radical 26 that bears the diphenylethyl radical in 3-exo-position, and is responsible for racemization. The 1-exo-3-endo-substituted allylic diradical 27 arises from the minor s-gaucheconformation of 22 and is capable of closing the three-or the five-membered ring, 22 or 23, respectively. The discussion centers on the question whether the allylic diradical is an intermediate or merely a TS. Quantum-chemical calculations by Houk et al. (1997) for the parent vinylcyclopropane reveal the lack of an intermediate. Can the conjugation of the allylic diradical with three Ph groups carve the well of an intermediate?

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“…UB3LYP was chosen, since unrestricted density functional theory, in addition to its capability to accurately describe heterolytic bond cleavage, turns out to work exceptionally well also for diradicalic singlet states resulting from homolytic bond cleavage, at comparably low computational cost. 30,31 To relax putative strain due to the previously applied Hartree-Fock level, 200 fs free density functional QM/MM MD were performed before switching on the flooding potential.…”

Section: Setupmentioning

confidence: 99%

Flooding in GROMACS: Accelerated barrier crossings in molecular dynamics

2006

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The major bottleneck of today's atomistic molecular dynamics (MD) simulations is that because of the enormous computational effort involved, only processes at nanoseconds to microseconds time scales or faster can be studied directly. Unfortunately, apart from a few exceptions, relevant processes, such as chemical reactions or many large scale conformational transitions in proteins, occur at slower time scales and therefore are currently far out of reach for conventional MD. The flooding technique addresses this problem by inclusion of a flooding potential into the force field. This flooding potential locally destabilizes the educt state and thereby significantly accelerates the escape from the initial energy well without affecting the reaction pathway. Here, we summarize the theory and method for the computational chemistry community and detail the implementation within the official version 3.3 of the freely available MD program package GROMACS. Two examples shall demonstrate the application of flooding to accelerate conformational transitions and chemical reactions. The second example was carried out within a QM/MM framework.

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Computational Explorations of Vinylcyclopropane−Cyclopentene Rearrangements and Competing Diradical Stereoisomerizations

Cited by 53 publications

References 41 publications

The Rearrangement of 2,2‐Diphenyl‐1‐[(E)‐2‐phenylethenyl]cyclopropane to 3,4,4‐Triphenylcyclopent‐1‐ene: a DFT Analysis

The Rearrangement of 2,2‐Diphenyl‐1‐[(E)‐2‐phenylethenyl]cyclopropane to 3,4,4‐Triphenylcyclopent‐1‐ene: a DFT Analysis

1‐[(E)‐2‐Arylethenyl]‐2,2‐diphenylcyclopropanes: Kinetics and Mechanism of Rearrangement to Cyclopentenes

Flooding in GROMACS: Accelerated barrier crossings in molecular dynamics

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