The meta photocycloaddition of arenes to alkenes

Cornelisse, J.

doi:10.1021/cr00018a002

Cited by 209 publications

(103 citation statements)

References 80 publications

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Section: Methodsmentioning

confidence: 93%

“…In the case of the unsubstituted reactants (benzene + ethylene), the wavelength of light used in experiments [26][27][28] suggests that the reaction proceeds via the lowest-lying singlet excited state of benzene 11,12,15,19,21,22,26 . In this case, the ratio of meta to ortho adduct is approximately 50:50 16,29 .There are only a few theoretical discussions of this reaction. Bryce-Smith and Gilbert have described the reaction mechanism of cycloadditions using orbital symmetry rules 14,15,30 .…”

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confidence: 97%

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How the Conical Intersection Seam Controls Chemical Selectivity in the Photocycloaddition of Ethylene and Benzene

et al. 2012

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The photocycloaddition reaction of benzene with ethylene has been studied at the CASSCF level, including the characterization of an extended conical intersection seam. We show that the regioselectivity is, in part, controlled by this extended conical intersection seam and that the shape of the conical intersection seam can be understood in terms of simple VB arguments. Further, the shape and energetics of the asynchronous segment of the conical intersection seam, suggests that 1,2 (ortho) and 1,3 (meta) will be the preferred regioselectivities with similar weight. The 1,4 (para) point on the conical intersection is higher in energy and corresponds to a local maximum on the seam. VB analysis shows that the pairs of VB structures along this asynchronous seam are the same and thus the shape will be determined mainly by steric effects. Synchronous structures on the seam are higher in energy and belong to a different branch of the seam separated by a saddle point on the seam. On S 1 we have documented three mechanistic pathways corresponding to transition states (with low barriers) between the reactants and the conical intersection seam: a mixed asynchronous/synchronous [1,2] ortho path, an asynchronous [1,3] meta path and a synchronous [1,3] meta path. 2 I IntroductionIn general, a photochemical reaction path has two branches: a branch on the excited state and a branch on the ground state. The two branches are connected at a point where the potential energy surfaces become degenerate known as a conical intersection (CI) [1][2][3][4][5][6][7] . However, a conical intersection is not an isolated point, but a collection of points, which we will refer to as a conical intersection "seam" 1,[8][9][10] . In this work we shall explore this feature in some depth for the case of the photochemical reactivity of ethylene and benzene. In the photocycloaddition of an arene and an alkene there are several possible regioselectivities (Scheme I). We will show that this regioselectivity is in part controlled by such an extended conical intersection seam.Experimental Background: Cycloadditions with alkenes are important and characteristic photochemical reactions of aromatic compounds. The prototype example of such a photocycloaddition is the reaction of benzene with ethylene [11][12][13][14][15][16][17][18][19][20][21][22] . Three cycloaddition modes (regioselectivity) can be distinguished (See Scheme 1): ortho-cycloaddition [1,2], meta-cycloaddition [1,3], and para-cycloaddition [1,4], and many applications of these reactions in organic synthesis have been described, as they afford the possibility to obtain polycyclic compounds in one step, which is important in the design of more complex molecular frameworks. Scheme 1 3The photocycloaddition reactions of arenes with alkenes have been extensively studied in order to rationalize the formation of the three possible cycloaddition products 11,16 . The meta-cycloaddition mode ([1,3] in our simplified notation) has been applied most extensively and is used as an important step in ...

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Section: Methodsmentioning

confidence: 93%

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confidence: 97%

How the Conical Intersection Seam Controls Chemical Selectivity in the Photocycloaddition of Ethylene and Benzene

et al. 2012

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“…The reactions of benzene, as well as its simple and multiply substituted derivatives were investigated in detail. Of the great number of review articles concerning arene photochemistry, only a few shall be mentioned here, in particular the excellent reviews (in the authors opinion) by Cornelisse and Hoffmann, [5,6] who present a selection of important cycloadditions. The contributions from the Leiden research group provide a particularly discerning and very good insight to date into the longdiscussed mechanism of photocycloadditions to benzene (Scheme 2).…”

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confidence: 99%

“…The contributions from the Leiden research group provide a particularly discerning and very good insight to date into the longdiscussed mechanism of photocycloadditions to benzene (Scheme 2). [5] The meta variation attracted the authors attention because of its unexpected pathway and its uncommon products. In the 1980s a universally valid model regarding the reaction mechanism was developed, and the effect of charge transfer on the periselectivity (ortho versus meta) as well as the influence of the substituents on the regio-and stereoselectivity could be resolved.…”

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Photochemistry of Arenes—Reloaded

Mattay¹

2007

Angew Chem Int Ed

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A question of time: The intramolecular meta photocycloaddition of naphthalene was only recently discovered, even though the corresponding additions to a simple benzene derivative have been known for a long time. The most important factor in the formation of the meta adduct is the irradiation time. The special features of the naphthalene structure finally give the opportunity for the stereoselective control of a meta photocycloaddition.

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Diastereoselective Intramolecular meta Photocycloaddition of Side-Chain-Substituted 5-(2-Methoxyphenyl)pent-1-enes

Timmermans

Wamelink

Lodder³

et al. 1999

Eur. J. Org. Chem.

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Irradiation of a series of 5‐(2‐methoxyphenyl)pent‐1‐enes substituted with a hydroxy or trimethylsilyloxy group at the α‐, β‐, or γ‐position of the side‐chain yields in all cases meta photocycloadducts, in which the configuration at the substituted carbon atom is mainly endo. This indicates that the diastereoselectivity originates from minimization of steric interactions between the side‐chain substituent and the ortho‐methoxy group at the arene unit. Hydrogen bonding does not seem to be involved. The introduction of the side‐chain substituents also influences the regioselectivity of the addition: The linear to angular adduct ratios are significantly increased compared to the case of the parent compound.

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The meta photocycloaddition of arenes to alkenes

Cited by 209 publications

References 80 publications

How the Conical Intersection Seam Controls Chemical Selectivity in the Photocycloaddition of Ethylene and Benzene

How the Conical Intersection Seam Controls Chemical Selectivity in the Photocycloaddition of Ethylene and Benzene

Photochemistry of Arenes—Reloaded

Diastereoselective Intramolecular meta Photocycloaddition of Side-Chain-Substituted 5-(2-Methoxyphenyl)pent-1-enes

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