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# Enediynes, enyne‐allenes, their reactions, and beyond

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Enediynes undergo a Bergman cyclization reaction to form the labile 1,4‐didehy‐drobenzene (p‐benzyne) biradical. The energetics of this reaction and the related Schreiner–Pascal reaction as well as that of the Myers–Saito and Schmittel reactions of enyne‐allenes are discussed on the basis of a variety of quantum chemical and available experimental results. The computational investigation of enediynes has been beneficial for both experimentalists and theoreticians because it has led to new synthetic challenges and new computational methodologies. The accurate description of biradicals has been one of the results of this mutual fertilization. Other results have been the computer‐assisted drug design of new antitumor antibiotics based on the biological activity of natural enediynes, the investigation of hetero‐ and metallo‐enediynes, the use of enediynes in chemical synthesis and materials science, or an understanding of catalyzed enediyne reactions. This article is categorized under: Structure and Mechanism > Molecular Structures
Bergman, Schreiner–Pascal, Myers–Saito, and Schmittel reaction of enediynes and enyne‐allenes.
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The impact of enediynes and enyne‐allenes on chemistry.
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Polymerization of enediynes.
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Metalloenediynes investigated to modulate the energetics of the Bergman reaction.
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Energetics of dynemicin (blue) versus dynemicin‐amidine (DAD; purple). (Reproduced from Ref . Copyright 2008, American Chemical Society.)
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The door handle principle of Kraka and Cremer illustrated for amidines and protonated amidines. (Reproduced from Ref . Copyright 2000, American Chemical Society.)
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Docking of dynemicin into the minor groove of DNA. (a) Insertion and (b) intercalation. (Reproduced from Ref . Copyright 2005, American Chemical Society.)
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Suggested strategies for biradical formation of an enediyne mimic or related compounds via a precursor at ambient conditions to yield DNA cleavage.
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Naturally occurring enediynes. For each enediyne, the warhead is given in red. For calicheamicin , the docking (blue box) and the triggering device (green box) are also indicated.
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Schematic representation of the state of p‐benzyne by a BS‐UDFT wave function. The HOMO–LUMO mixing is given schematically where the form of the frontier orbitals has been simplified to local orbitals and .
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Frontier orbitals of p‐benzyne (in blue), which result from through‐bond interactions involving the singly‐occupied orbitals (on the left) and the / orbitals (on the right).
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Schematic representation of wave function and energy of type 0, type I, type II, and type III electronic systems as described by RDFT or UDFT with approximate exchange‐correlation functionals (dotted lines) or exact Kohn–Sham DFT (solid line). Numbers 0, 1, 2, etc. denote CSF Ψ0, Ψ1, Ψ2, etc. or determinants Φ0, Φ1, etc. The weights w of the CSF in the true wave function are schematically shown (first row of diagrams) in dependence of the parameter λ that stepwise increases the electron correlation energy from zero (λ = 0) to its true value (λ = 1). The corresponding changes in the Kohn–Sham energy and in the exact energy E(exact) (blue) are schematically given in the second row of diagrams. For each type of electronic system, a molecular representative is given at the bottom where one of several electron configurations is indicated. (Reproduced from Ref . Copyright 2002, MDPI.)
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Acyclic enediynes undergoing the Bergman cyclization at either room temperature (RT) or reduced temperature. Temperatures are in °C are given below formulas.
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Electronic effects determining the energetics of the Bergman cyclization (see the text).
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Influence of strain effects on the barrier of the Bergman cyclization.
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Change in the critical distance C2, C7 (corresponding to C1, C6 in 1) before and after opening of the epoxide in dynemicin A.
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Dependence of the activation enthalpy of the Bergman cyclization of (Z)‐hex‐3‐ene‐1,5‐diyne on the critical distance between carbon atoms C1 and C6 according to ab initio calculations (black dots). Known C1C6 distances, measured activation enthalpies (starred values), half‐life times , and cyclization temperatures are also given. The deviations of the starred values indicate the limitations of the ab initio relationship. (Reproduced with permission from Ref . Copyright 1994, American Chemical Society.)
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Energetics of the Bergman cyclization of (Z)‐hex‐3‐ene‐1,5‐diyne 1 as determined by experiment. The experimental reaction enthalpy , the activation enthalpies for forward and backward reaction, and , respectively, are converted to both enthalpy differences at 298 K and energy differences at 0 K (, , ) using vibrational corrections calculated at the B3LYP/6‐311+G(3df,3pd) level of theory. (Reproduced with permission from Ref . Copyright 2000, American Chemical Society.)
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