Effect of .alpha.-methyl groups on the photochemistry of 3,4,5,6,7,8-hexahydronaphthalen-2(1H)-one

Engel, Paul S.; Schexnayder, Mary A.; Ziffer, Herman; Seeman, Jeffrey I.

doi:10.1021/ja00810a051

Cited by 28 publications

(14 citation statements)

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“…However, this selectivity is not universal, and the reasons for this are not fully understood. In some cases the [1,3]-acyl shift product is also formed on triplet sensitization, while the ODPM rearrangement product has been observed on direct photolysis of certain enones. − Nowadays it is generally accepted that the [1,3]-acyl shift occurs from an nπ* excited state in either the singlet (S 1 ) or triplet (T 2 ) manifold, while the ODPM rearrangement originates from the slightly lower energy triplet ππ* state (T 1 ) where the excitation is localized on the alkene moiety. , The energy difference between the two triplet states is thought to be as little as 2 kcal mol -1 . Both rearrangements have been the subject of several reviews, 12a,, and the possible reaction mechanisms have been summarized in Scheme .…”

Section: Introductionmentioning

confidence: 99%

Mechanism of the Oxadi-π-methane and [1,3]-Acyl Sigmatropic Rearrangements of β,γ-Enones: A Theoretical Study

et al. 1996

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The oxadi-π-methane ([1,2]-acyl shift) and [1,3]-acyl shift rearrangements of a simple β,γ-enone (but-3-enal) have been investigated using MC-SCF computations in a 6-31G* basis set. The excited state reaction pathways and decay funnels for this model compound can be used to explain the direct and triplet-sensitized photochemistry of β,γ-enones in general. Our calculations show that the “classical” biradical intermediates proposed for both reactions correspond to decay funnels at which four states (S1(nπ*), T1(ππ*), T2(nπ*), and S0) are degenerate. Both efficient internal conversion (IC) and efficient intersystem crossing (ISC) can occur at these points, and the ground state reaction path is therefore the same regardless of the state initially populated. The ratio of products formed on photolysis is governed by the relative heights of the barriers leading to these decay funnels, and these will be sensitive to substituent effects on the reactant molecule. The oxadi-π-methane rearrangement is found to occur via a three-step process, where the four-level decay funnel corresponds to the first of two floppy intermediates on S0. There are two possible mechanisms leading to the [1,3]-acyl shift product: one involving the four-level decay funnel which corresponds to a “tight” intermediate in a quasi-concerted pathway, and a second which involves dissociation and recombination.

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Section: Introductionmentioning

confidence: 99%

Mechanism of the Oxadi-π-methane and [1,3]-Acyl Sigmatropic Rearrangements of β,γ-Enones: A Theoretical Study

et al. 1996

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“…This is at variance with the results obtained by Luibrand et al12 in their sensitized irradiation of bicyclic octenone 11 , which generated a DPM photoproduct. The presence of the methyl group at the bridgehead carbon atom may have enhanced the reactivity of the α‐cleavage process that may occur during singlet (S 1 , n,π*) or triplet (T 2 , n,π*) excitation by stabilization of the incipient radical generated at the bridgehead carbon atom 2,20,26b. Interestingly, the bicyclodienones 1b and 1c did not undergo rearrangement under triplet‐sensitization conditions.…”

Section: Discussionmentioning

confidence: 99%

Photochemical Reactions of 1,3,3‐Trimethylbicyclo[2.2.2]octa‐5,7‐dien‐2‐ones

et al. 2006

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The photochemistry of 1,3,3-trimethylbicyclo[2.2.2]octa-5,7-dien-2-ones 1a-f containing multiple chromophoric moieties under various conditions is described. Upon direct irradiation, dienones 1a-f in benzene, acetonitrile, and methanol were found to aromatize through photoelimination of dimethylketene, which was trapped with 3-phenylprop-2-en-1-ol (12). Triplet sensitization of dienone 1a in acetone and in acetone/acetophenone mixed solvents afforded aromatic compound 2a, whilst bicyclic systems 1b-c were found to be

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“…The magnitude of the upfield shift upon Z → E isomerization is larger than that in the methyl and ethyl analogues . Irradiation of 4b Z at ambient temperature and 313 nm in acetone- d 6 as solvent and triplet sensitizer − exhibited the same rearrangement quantum yield as in toluene- d 8 . Irradiationof 4b Z in toluene at −53 °C in the ESR cavity led to a weak signal about 50 G wide consisting of 13 peaks, which were much broader than those from 4a .…”

Section: Resultsmentioning

confidence: 89%

Photorearrangement of α-Azoxy Ketones and Triplet Sensitization of Azoxy Compounds

et al. 2005

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[reaction: see text] Although some aspects of azoxy group radical chemistry have been investigated, unhindered alpha-azoxy radicals remain poorly understood. Here we report the generation of alpha-azoxy radicals under mild conditions by irradiation of alpha-azoxy ketones 4a,b. These compounds undergo alpha-cleavage to yield radicals 5a,b, whose oxygen atom then recombines with benzoyl radicals to produce presumed intermediate 15. Formal Claisen rearrangement gives alpha-benzoyloxyazo compounds 8a,b, which are themselves photolabile, leading to both radical and ionic decomposition. The ESR spectrum of 5a was simulated to extract the isotropic hyperfine splitting constants, which showed its resonance stabilization energy to be exceptionally large. Azoxy compounds have been found for the first time to be good quenchers of triplet excited acetophenone, the main sensitized photoreaction of 7Z in benzene being deoxygenation. While this reaction has been reported previously, it was always in hydrogen atom donating solvents, where chemical sensitization occurred. The principal direct irradiation product of 4bZ and model azoxyalkane 7Z is the E isomer, whose thermal reversion to Z is much faster than that of previously studied analogues.

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Effect of .alpha.-methyl groups on the photochemistry of 3,4,5,6,7,8-hexahydronaphthalen-2(1H)-one

Cited by 28 publications

References 0 publications

Mechanism of the Oxadi-π-methane and [1,3]-Acyl Sigmatropic Rearrangements of β,γ-Enones: A Theoretical Study

Mechanism of the Oxadi-π-methane and [1,3]-Acyl Sigmatropic Rearrangements of β,γ-Enones: A Theoretical Study

Photochemical Reactions of 1,3,3‐Trimethylbicyclo[2.2.2]octa‐5,7‐dien‐2‐ones

Photorearrangement of α-Azoxy Ketones and Triplet Sensitization of Azoxy Compounds

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