Computational Studies on the Electrocyclizations of 1-Amino-1,3,5-hexatrienes

Güner, V.; Houk, K. N.; Davies, Ian W.

doi:10.1021/jo048540s

Cited by 33 publications

(14 citation statements)

References 28 publications

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“…Herein, we report the first examples of catalytic 6p electrocyclizations and provide a detailed investigation into the mechanism of these reactions.Experimental and computational studies have shown that the rate of 6p electrocyclizations can be influenced by varying the electronics of the substituents on the triene. [4][5][6][7] Electron-withdrawing groups located in the 2-position of hexatriene systems have been observed to lower their electrocyclization energy barriers, [6,7] sometimes by as much as 10 kcal mol À1 . [7,8] We envisioned exploiting this effect to catalyze 6p electrocyclizations by the coordination of a Lewis acid to a Lewis basic electron-withdrawing group located in the 2-position of a hexatriene system.…”

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confidence: 99%

“…[4][5][6][7] Electron-withdrawing groups located in the 2-position of hexatriene systems have been observed to lower their electrocyclization energy barriers, [6,7] sometimes by as much as 10 kcal mol À1 . [7,8] We envisioned exploiting this effect to catalyze 6p electrocyclizations by the coordination of a Lewis acid to a Lewis basic electron-withdrawing group located in the 2-position of a hexatriene system. This coordination should increase the electron-withdrawing effect of the substituent, thereby decreasing the electrocyclization energy barrier.We began our investigations by computationally assessing the viability of this approach in the catalysis of 6p electrocyclizations.…”

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Catalysis of 6π Electrocyclizations

et al. 2008

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The synthetic power of pericyclic reactions has greatly increased with the emergence of catalytic variants. Indeed, catalysis in cycloadditions [1] and sigmatropic rearrangements [2] is now well established. General methods for the catalysis of electrocyclizations, however, have remained elusive, with the notable exception of the Nazarov cyclization.[3] The development of such methods would enable electrocyclizations to occur under milder conditions and create the possibility of catalytic asymmetric variants. Herein, we report the first examples of catalytic 6p electrocyclizations and provide a detailed investigation into the mechanism of these reactions.Experimental and computational studies have shown that the rate of 6p electrocyclizations can be influenced by varying the electronics of the substituents on the triene. [4][5][6][7] Electronwithdrawing groups located in the 2-position of hexatriene systems have been observed to lower their electrocyclization energy barriers, [6,7] sometimes by as much as 10 kcal mol À1 . [7,8] We envisioned exploiting this effect to catalyze 6p electrocyclizations by the coordination of a Lewis acid to a Lewis basic electron-withdrawing group located in the 2-position of a hexatriene system. This coordination should increase the electron-withdrawing effect of the substituent, thereby decreasing the electrocyclization energy barrier. We began our investigations by computationally assessing the viability of this approach in the catalysis of 6p electrocyclizations. Hexatriene systems with methyl ester substituents at all possible positions and orientations were modeled by density functional theory (Figure 1). A proton, serving as the simplest Lewis acid, was bonded to the carbonyl oxygen atom at the lone pair anti to the hexatriene.[9] As seen in Figure 1, these calculations predict a slight increase and decrease of the electrocyclization energy barrier for the (E,Z)-and (Z,Z)-1-carbomethoxy-substituted hexatriene systems (Figure 1 A and B), respectively. Calculations additionally predict a small decrease of the electrocyclization energy barrier for the 3-substituted system (Figure 1 D). However, we found that the electrocyclization energy barrier is predicted to decrease by 10 kcal mol À1 upon protonation of the 2-carbomethoxy-substituted triene system (Figure 1 C). An intrinsic reaction coordinate search in both directions from the protonated electrocyclization transition state of this system suggests that the catalyzed pathway is a concerted process, as no stationary points other than the transition state were located between the protonated triene and protonated cyclohexadiene.

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Catalysis of 6π Electrocyclizations

et al. 2008

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“…Next, energy decomposition strategy was used to explore the origin of the activating effect for directed C–H activation by strong acid [ 63 , 75 , 76 , 77 , 78 ]. As shown in Scheme 5 , ΔG TS ≠ can be decomposed into two parts: ΔG 1 and ΔG 2 ≠ .…”

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confidence: 99%

The Activating Effect of Strong Acid for Pd-Catalyzed Directed C–H Activation by Concerted Metalation-Deprotonation Mechanism

Jiang

Sun

2021

Molecules

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A computational study on the origin of the activating effect for Pd-catalyzed directed C–H activation by the concerted metalation-deprotonation (CMD) mechanism is conducted. DFT calculations indicate that strong acids can make Pd catalysts coordinate with directing groups (DGs) of the substrates more strongly and lower the C–H activation energy barrier. For the CMD mechanism, the electrophilicity of the Pd center and the basicity of the corresponding acid ligand for deprotonating the C–H bond are vital to the overall C–H activation energy barrier. Furthermore, this rule might disclose the role of some additives for C–H activation.

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“…Furthermore, to the best of our knowledge, 6π electrocyclization of hexatrienes was relatively disfavored to give 1,3‐cyclohexadiene with a free energy of activation ΔG ≠ of 30.7 kcal⋅mol −1 at 298 K [see Supporting Information, Scheme S1 (a)] and could proceed under thermodynamic and photochemical conditions for application in natural products synthesis 17. A study towards understanding the thermodynamics and kinetics of the 6π electrocyclization of 1‐dimethylamino‐1,3,5‐hexatriene relevant to substitution effects by hybrid density functional calculations revealed a decreased activation barrier of 17–25 kcal⋅mol −1 by placement of an electron‐withdrawing group (EWG) at C‐2 18. Significant findings through the two‐layer ONIOM method by Fu and Liu suggested approaches to promote the sluggish electrocyclization of 1,3,5‐hexatrienes by specific captodative substitution 19.…”

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confidence: 99%

Multicomponent Reactions of Phosphines, Enynedioates and Cinnamaldimines Give γ‐Lactams with a 1,3,5‐Hexatriene Moiety for Facile 6π Electrocyclization: Access to Oxindoles, Isatins and Isoxazolinones

et al. 2015

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Multicomponentr eactions of phosphines, enynedioates andc innamaldiminesg enerated 3phosphorus ylide g-lactamsh aving a1 ,3,5-hexatriene moiety with low activation energy barrier for 6p electrocyclization, through initial formation of 1,3-dipoles from the a(d')-Michael addition of phosphines to enynedioates.T he reactive 1,3-dipoles underwent addition to cinnamaldimines, lactamization, 6p electrocyclization ando xidation to give3 -phosphorus ylide oxindoles as platform molecules toward isatins and isoxazolinones.T he keys tep,6 pelectrocyclization, wasfurther examined by akinetic and acomputational study.Scheme 1. Tr aditional and our proposed synthetic strategy toward oxindoles 5.

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Computational Studies on the Electrocyclizations of 1-Amino-1,3,5-hexatrienes

Cited by 33 publications

References 28 publications

Catalysis of 6π Electrocyclizations

Catalysis of 6π Electrocyclizations

The Activating Effect of Strong Acid for Pd-Catalyzed Directed C–H Activation by Concerted Metalation-Deprotonation Mechanism

Multicomponent Reactions of Phosphines, Enynedioates and Cinnamaldimines Give γ‐Lactams with a 1,3,5‐Hexatriene Moiety for Facile 6π Electrocyclization: Access to Oxindoles, Isatins and Isoxazolinones

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