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- W1607429521 abstract "Le dimère 3trans du triphényl-allène 1 donne par ouverture thermique conrotatoire le diradical 2Z,Z. Cet intermédiaire peut conduire, par les deux refermetures possibles (mode a ou b) en ortho de ses substituants phényles, aux composés bicycliques 4a et 4b. La preuve de l'existence d'un équilibre entre le dimère 3 trans et ses isomères moins stables 4a et 4b est apportée par la formation des dérivés naphtaléniques 9a et 9b lorsque la réaction est effectuée en présence de bases fortes, qui provoquent les prototropies irréversibles 4 → 9. Avec une base faible telle que la quinoléine, l'isomérisation des polyènes4a et 4b se limite à un passage à leurs isomères 8a et 8b. Ces derniers intermédiaires se cyclisent ensuite thermiquement, de façon classique, pour conduire respectivement aux dérivés tétracycliques 12 cis et 11b. L'intervention d'un tel équilibre entre 3 trans et 4a,b rend compte de l'obtention précédemment décrite du dihydronaphtacène 14, dans le cas précis du triphényl-allène 1, et confirme, de manière plus générale, le mécanisme récemment proposé pour expliquer la formation de dérivés naphtacéniques à partir des polyphényl-allènes chlorés (réaction rubrénique). Thermal opening of the 3 trans dimer of triphenylallene 1 is conrotatory, and generates the diradical 2Z,Z. This intermediate, through ortho reclosures involving the two types of substituing phenyl groups (modes a or b), can lead to the bicyclic compounds 4a and 4b. The existence of an equilibrium between the 3 trans dimer and its less stable isomers 4a and 4b is substantiated by the formation of naphthalenic derivatives 9a and 9b when the reaction is carried out in the presence of strong bases, which give rise to irreversible prototropic shifts 4 → 9. A weak base such as quinoline allows only a less complete isomerization of polyenes 4a and 4b, leading to their isomers 8a and 8b. The latter then thermally cyclize, in a classical way, and lead respectively to the tetracyclic compounds 12 cis and 11b. The occurrence of such an equilibrium between 3 trans and 4a,b accounts for the previously reported obtention of the dihydronaphthacene 14, in the precise instance of triphenyl-allene 1 dimerization, and more generally corroborates the recently proposed mechanism of naphthacenic compounds production from chlorinated polyphenyl-allenes." @default.
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- W1607429521 date "1979-01-01" @default.
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- W1607429521 title "Dimerisation des polyphenyl-allenes—III" @default.
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- W1607429521 doi "https://doi.org/10.1016/0040-4020(79)87024-6" @default.
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