Stereoselective substituent effects on conrotatory electrocyclic reactions of cyclobutenes

Kirmse, Wolfgang; Rondan, Nelson G.; Houk, K. N.

doi:10.1021/ja00337a067

Cited by 257 publications

(121 citation statements)

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“…This behaviour can be correlated to the classic torquoelectronic effect observed by Houk in the conrotatory opening-closure of four-membered rings. [8] The torquoelectronic effect is due to an interaction between the p orbitals of the substituent and the σ-forming bond in the transition state, and it is destabilizing when a donor group is placed in the inward position and stabilizing when a donor group is placed in the outward position. [9] In fact, in Table 1 the relative energies point out a decrease in the outward transition state energy (and related activation energy) and an increase of the inward transition state energy (and related activation energy) going from the trifluoromethyl group, which has the minimum donor effect in the series, to the amino group, which has the maximum donor effect.…”

Section: Resultsmentioning

confidence: 99%

An Ab Initio Study of Substituent Effects on the Electrocyclization of Silyloxyazadienes

2007

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The electrocyclization of 4‐substituted 3‐silyloxy‐2‐azadienes to β‐lactams was studied at the MP2/6‐31G* level of theory and the effect of the substituents on the reactivity of the azadiene and on the stereochemistry of the cyclic products was evaluated. It was shown that the electrocyclization is favoured when the substituent in 4‐position is in the (Z) configuration and discloses an electron‐donor effect. The cyclization reactions generally lead to trans β‐lactams, but with a basic substituent cis β‐lactams are obtained as well.(© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2007)

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Section: Resultsmentioning

confidence: 99%

An Ab Initio Study of Substituent Effects on the Electrocyclization of Silyloxyazadienes

2007

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“…[95] (Z,Z) (E,E) (in,in) (out,out) Rondan and Houk proposed in 1984 a widely accepted orbital model able to explain torquoselectivity. [96,97] In a nutshell, this model states that electron donor substituents at C 3 and C 4 preferentially rotate outward in order to maximize the stabilizing interaction with the HOMO of the breaking C 3 -C 4 bond and to minimize the repulsive interaction with the LUMO of the same bond. Electron acceptor substituents undergo the opposite effect, and, consequently, inward rotation is preferred.…”

Section: Reactivitymentioning

confidence: 99%

A Complete NCI Perspective: From New Bonds to Reactivity

Narth¹,

Maroun²,

Boto³

et al. 2016

Challenges and Advances in Computational Chemistry and Physics

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The Non-Covalent Interaction (NCI) index is a new topological tool that has recently been added to the theoretical chemist's arsenal. NCI fills a gap that existed within topological methods for the visualization of non-covalent interactions. Based on the electron density and its derivatives, it is able to reveal both attractive and repulsive interactions in the shape of isosurfaces, whose color code reveals the nature of the interaction. It is interesting to note that NCI can even be calculated at the promolecular level, making it a suitable tool for big systems, such as proteins or DNA. Within this chapter we will review the main characteristics of NCI, its similarities with and differences from previous approaches. Special attention will be paid to the visualization of new interaction types. Being based on the electron density, NCI is not only very stable with respect to the calculation method, but it is also a suitable tool for detecting new bonding mechanisms, since all such mechanisms should have a detectable effect on the electron density. This type of approach overcomes the limitations of bond definition, revealing all interaction types, irrespective of whether they have a name or have previously been identified. Finally, we will show how this tool can be used to understand chemical change along a chemical reaction. We will show several examples of torquoselectivity and put forward an explanation of selectivity based on secondary interactions which is complementary to the historical orbital approach.A complete NCI perspective: from new bonds to reactivity 3

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“…[14] We rationalized that in order to control the absolute direction of rotation of the orbitals in the ringclosing process (the torquoselectivity), [15] we needed to block one p-face of the delocalized anionic component of the reaction and rely on the stereospecificity of the electrocyclic process to direct the stereochemical outcome (Scheme 1 B). One way to accomplish this would be to exploit tight ionpairing in an organic solvent, using a chiral counterion to select one of the two faces of a pentadienyl anion or equivalent, and hence influence the enantioselectivity of the cyclization reaction.…”

mentioning

confidence: 99%

Catalytic Asymmetric 6π Electrocyclization: Enantioselective Synthesis of Functionalized Indolines

2009

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Pericyclic reactions are a class of transformations that comprise sigmatropic rearrangements, group transfer reactions, cycloadditions and electrocyclic reactions. Since Woodward and Hoffmann delineated a rationale for the mechanism and stereochemistry of these reactions, they have become powerful synthetic tools. [1][2][3] Whilst sigmatropic rearrangements and cycloadditions are cornerstones of contemporary synthetic methodology, many electrocyclic reactions are not fully exploited. The high temperatures often required to initiate these transformations, and difficulties associated with assembling polyene precursors, often preclude their use in complex-molecule synthesis. There are no general methods for the asymmetric catalysis of electrocyclic reactions, and as a consequence opportunities for exerting stereocontrol in these manifolds are limited. [4,5] The archetypal 6p electrocyclic reaction-the hexatriene cyclization-proceeds suprafacially, and isoelectronic charged systems such as pentadienyl anion derivatives electrocyclize through the same mode (Scheme 1 A). [6,7] We reasoned that exploring these anionic manifolds could provide an opportunity for exerting stereocontrol in an electrocyclic reaction. Here we describe this approach, and outline a catalytic asymmetric process for the generation of functionalized indolines. [8] It has been demonstrated that the rates of electrocyclization of both 6p and 8p systems are dependant on the nature of the substituents in and around the extended p-system. Synergistic combinations of electron-withdrawing and donating groups have been demonstrated to significantly lower the barrier to cyclization.[9] Similarly, the presence and positioning of heteroatoms within the p-system is known to have profound effects on the propensity for cyclization.[10] In a series of pioneering investigations by Speckamp et al.[11] and others, [12] the [1,5]-electrocyclic reaction [13] of 2-aza-pentadienyl anions has been demonstrated to be a powerful and efficient process. [14] We rationalized that in order to control the absolute direction of rotation of the orbitals in the ringclosing process (the torquoselectivity), [15] we needed to block one p-face of the delocalized anionic component of the reaction and rely on the stereospecificity of the electrocyclic process to direct the stereochemical outcome (Scheme 1 B). One way to accomplish this would be to exploit tight ionpairing in an organic solvent, using a chiral counterion to select one of the two faces of a pentadienyl anion or equivalent, and hence influence the enantioselectivity of the cyclization reaction. Asymmetric phase-transfer catalysis [16] relies on the tight-ion pairing principle, and has been demonstrated to be a powerful and practical approach to the generation of enantioenriched materials. As a consequence, we examined a series of cinchona alkaloid-derived quaternary ammonium salts 1-6 as chiral counterions for our approach to asymmetric electrocyclization (Scheme 2). [17] We prepared a series of model benzaldimines 7-9 (a...

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Stereoselective substituent effects on conrotatory electrocyclic reactions of cyclobutenes

Cited by 257 publications

References 1 publication

An Ab Initio Study of Substituent Effects on the Electrocyclization of Silyloxyazadienes

An Ab Initio Study of Substituent Effects on the Electrocyclization of Silyloxyazadienes

A Complete NCI Perspective: From New Bonds to Reactivity

Catalytic Asymmetric 6π Electrocyclization: Enantioselective Synthesis of Functionalized Indolines

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