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WIREs Comput Mol Sci
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The Cope rearrangement—the first born of a great family

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This review takes the experimental and theoretical discussions on the Cope rearrangement as the basis to emphasize its tight connection to many closely related pericyclic reactions. The Cope reaction, which is rather simple in a formal sense, has led to a plethora of mechanistic discussions to determine the nature of biradical‐like intermediates or transition structures. After intense experimental and theoretical investigations starting in the late 1960s, the Cope rearrangement turned out to be a multifaceted reaction with a ‘chameleonic’ nature, ranging from homoaromatic transition structures to biradical intermediates in substituted cases, and six‐electron transition states in the parent system. Additionally, the Cope rearrangement served as an excellent example to probe theoretical methods for the computations of a variety of pericyclic reactions. However, the relationship of the Cope rearrangement with analogous reactions has been hampered by the notion that pericyclic reactions typically are assumed to proceed in a concerted fashion. Only in the past 10 years, the Cope reaction, with its 1,5‐hexadiene unit, emerged as the structural and mechanistic prototype of a large family, including sigmatropic, cycloaddition, and other electrocyclic reactions as well as thermal rearrangements of polyunsaturated systems, enediynes, eneyne‐allenes, and many others. The recurrent and interconnecting motif in this family of reactions is the questions regarding cyclic aromatic transition states and the possible involvement of biradical intermediates. © 2011 John Wiley & Sons, Ltd. WIREs Comput Mol Sci 2011 1 172‐190 DOI: 10.1002/wcms.17

Figure 1.

Stereospecificity of the Cope rearrangement.

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Figure 2.

Resonance contributions to the transition state of the Cope rearrangement.

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Figure 3.

More O'Ferrall‐Jencks plot of the Cope reaction depending on substitutents.

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Figure 4.

Chameleonic and centauric model of substituted Cope rearrangements (experimental Ea in kcal mol−1).37,44,50

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Figure 5.

Strained Cope derivatives.

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Figure 6.

Stabilization of the bishomoaromatic structure of barbaralane in dipolar and polarizable solvents (ΔG = Gibbs free energy difference in N,N‐dimethylpropylene urea).83

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Figure 7.

The Cope reaction of stelladiene derivatives.85

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Figure 8.

Thermally allowed pericyclic reaction—variations I of the Cope framework.

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Figure 9.

Variations II of the Cope framework.

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Figure 10.

Different types of reactions in the Cope family.

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Figure 11.

Yet‐to‐be observed Cope‐type reactions.

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Electronic Structure Theory > Density Functional Theory
Theoretical and Physical Chemistry > Reaction Dynamics and Kinetics
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