Flash vacuum pyrolysis of benzylidene halides, benzotrihalides and aryl halides over magnesium
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Flash vacuum pyrolysis at 600 °C through glass wool coated with freshly sublimed magnesium is examined as a preparative method for dehalogenative coupling in organic synthesis. Substituted benzylidene chlorides give predominantly the corresponding stilbenes and in some cases these are readily isolated in pure form. With an ortho-halogen substituent, additional cyclisation gives phenanthrenes but the method is not compatible with the presence of several reactive groups. An ortho-methoxy substituent leads to unexpected formation of mono- and dimethyl products. With 1,4-bis(dihalomethyl)benzenes, halogenated polymers are deposited directly from the gas phase via generation of halogenated p-xylylenes. The 1,2- and 1,3-isomers lead respectively to benzocyclobutadiene, isolated as a dimer, and to pyrene. The 1,4-bis(trihalomethyl)benzenes give more highly halogenated polymers directly from the gas phase via halogenated p-xylylenes. While halobenzenes generally give the corresponding benzenes and biphenyls, 1,2-dihalobenzenes additionally produce triphenylene in preparatively useful yield by a process not involving intermediacy of free benzyne.
Aitken , R A , Hodgson , P K G & Oyewale , A O 2017 , ' Flash vacuum pyrolysis of benzylidene halides, benzotrihalides and aryl halides over magnesium ' Journal of Analytical and Applied Pyrolysis , vol 124 , pp. 618-630 . DOI: 10.1016/j.jaap.2016.12.028
Journal of Analytical and Applied Pyrolysis
© 2016 Elsevier B.V. All rights reserved. This work has been made available online in accordance with the publisher’s policies. This is the author created, accepted version manuscript following peer review and may differ slightly from the final published version. The final published version of this work is available at: https://doi.org/10.1016/j.jaap.2016.12.028
This work was supported by B.P.
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