Photoreaktion von 3,6‐Dihydrophthalsäureanhydrid mit Alkinen

Askani, R.; Hoffmann, Jochen

doi:10.1002/cber.19911241025

Cited by 2 publications

(2 citation statements)

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“…Since the earlier homoquadricyclane structures were suggested exclusively from NMR spectra, , X-ray crystallographic analysis of compounds 19 and 22 for the first time unambiguously confirmed the homoquadricyclane structure of the products. This analysis also revealed interesting structural features of the [3.3.0.0 2,8 .0 4,6 ]octane moiety.…”

Section: Resultsmentioning

confidence: 82%

“…Literature data suggest that the competition between the [2+2] and homoquadricyclane pathways is sensitive to the structure of the reagents. For example, although photocycloaddition of several acetylenes to a carboxyl substituted cyclohexadiene also leads to homoquadricyclanes, , the reaction of diphenyl acetylene proceeds mainly through the [2+2] pathway (Scheme ). Even though the factors controlling the competition between the two pathways remain unknown, the regiochemistry of [2+2] cycloadditions suggests that they are likely to proceed through an excited state of the diene where the excitation is concentrated at the double bond conjugated with the carbonyl groups.…”

Section: Introductionmentioning

confidence: 99%

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Triplet Acetylenes as Synthetic Equivalents of 1,2-Bicarbenes: Phantom n,π* State Controls Reactivity in Triplet Photocycloaddition

et al. 2005

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Diaryl acetylenes, in which one of the aryl groups is either a pyridine or a pyrazine, undergo efficient triplet state photocycloaddition to 1,4-cyclohexadiene with formation of 1,5-diaryl substituted tetracyclo[3.3.0.0(2,8).0(4,6)]octanes (homoquadricyclanes). In the case of pyrazinyl acetylenes, the primary homoquadricyclane products undergo a secondary photochemical rearangement leading to diaryl substituted tricyclo[3.2.1.0(4,6)]oct-2-enes. Mechanistic and photophysical studies suggest that photocycloaddition proceeds through an electrophilic triplet excited state whereas the subsequent rearrangement to the tricyclooctenes proceeds through a singlet excited state. Chemical and quantum yields for the cycloaddition, in general, correlate with the electron acceptor character of aryl substituents but are attenuated by photophysical factors, such as the competition between the conversion of acetylene singlet excited state into the reactive triplet excited states (intersystem crossing: ISC) and/or to the radical-anion (photoelectron transfer from the diene to the excited acetylene: PET). Dramatically enhanced ISC between pi-pi S(1) state and "phantom" n,pi triplet excited state is likely to be important in directing reactivity to the triplet pathway. The role of PET can be minimized by the judicious choice of reaction conditions (solvent, concentration, etc.). From a practical perspective, such reactions are interesting because "capping" of the triple bond with the polycyclic framework orients the terminal aryl (4-pyridyl, 4-tetrafluoropyridyl, phenyl, etc.) groups in an almost perfect 60 degrees angle and renders such molecules promising supramolecular building blocks, especially in the design of metal coordination polymers.

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Section: Resultsmentioning

confidence: 82%

Section: Introductionmentioning

confidence: 99%