Photoreaction of benzene with 1,2-dichloroethylenes

Bryce‐Smith, D.; Foulger, B. E.; Gilbert, Andrew

doi:10.1039/c39720000769

Cited by 8 publications

(4 citation statements)

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“…The latter effect causes fluorine to appear at the center position of the allylic moiety in the polarized intermediate and from thence at b3 in the adduct. Only one photoaddition with chlorobenzene has been reported (Table 2, entry 61), and chlorine evidently behaves as an electron-donating group.…”

Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

“…This was tried with a cyano group at position 3 (<5~) as well as with a fluorine atom at C-4 or C-6 (next to 5'), but it was to no avail. The 2-fluoro compound (Table 4, entry 49) underwent only 1,3 addition, the 3-cyano compound (Table 4, entry 61) did not give meta photoadducts at all, and the 4-fluoro analogue (Table 4, entry 70) gave a high yield of the 2,6 adduct, but only after the starting material had isomerized to trans! When this escape route was blocked by using the dimethyl derivative (Table 4, entry 71) the compound underwent only ortho addition.…”

Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

“…There are some exceptions to the rule that cyclopentene prefers to give adducts with the endo configuration. More exo than endo is found with mcyano-a,a,a-trifluorotoluene (Table 3, entry 52), mbis(trifluoromethyl)benzene (Table 3, entry 56), o-fluorotoluene (Table 3, entry 61), and p-difluorobenzene (Table 3, entry 65). Relatively large percentages of exo (>30%) are found with a,a,a-trifluorotoluene (Table 2, entry 62), benzonitrile (Table 2, entry 68), p-cyanoa,a,a-trifluorotoluene (Table 3, entry 54), m-fluorotoluene (Table 3, entry 62), /n-difluorobenzene (Table 3, entry 64), and 1,3,5-trifluorobenzene (Table 3, entry 66).…”

Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

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The meta photocycloaddition of arenes to alkenes

Cornelisse¹

1993

Chem. Rev.

203

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Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

Section: Regioselectivity Stereoselectivitymentioning

confidence: 99%

See 1 more Smart Citation

The meta photocycloaddition of arenes to alkenes

Cornelisse¹

1993

Chem. Rev.

203

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“…Ortho addition is preferred when there is a substantial difference between the electron-donor and electron-acceptor properties of the arene and the alkene, and meta when these differences are small. Finally, the [1,4] pathway takes place in a very few cases where the steric factors are important 16 or when the alkene is an allene 23 or a diene 24,25 . 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 .…”

Section: Methodsmentioning

confidence: 99%

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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