Helical Atropisomers of Strained Phenanthrenes by Photochemistry of Aromatic Pauson-Khand Cycloadducts

[摘要]：Norbornene and norbornadiene PausonKhand adducts of bis(3,5-dimethylphenyl)acetylene and bis(3,4,5-trimethylphenyl)acetylene were prepared. These compounds were subjected to a photochemical 6p-electrocyclic oxidative aromatization reaction to give the corresponding phenanthrene compounds in satisfactory yield in the case of norbornene derivatives. The helical twist imposed by the methyl groups at the 3- and 5-positions on the aromatic rings led to two atropisomers as a result of the non-planar helical phenanthrene structure. The molecular structures and conformational stabilities of these atropisomers were examined by X-ray crystallography and variable temperature NMR studies.

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