Abstract
o-Quinodimethane can be generated from α,α'-dihalo-o-xylenes using zinc in aqueous solution. In the presence of activated dienophiles cycloadducts can be obtained directly. Catalysis with tris-triphenylphosphine ruthenium(II) dichloride reduces side reactions such as reduction and polymerisation and improves the yield. This is the first example of an organometallic cyclisation in aqueous medium using dihalo compounds.
Highlights
Introduction o-Quinodimethanes (o-xylylenes) are reactive intermediates widely used for the synthesis of polycyclic compounds via inter- or intramolecular Diels-Alder reactions [1]
The reaction of the dibromo compound 1a with zinc dust in saturated aqueous ammonium chloride was complete in a few minutes at r.t. and produced a polymeric material 3 containing 67 % of C-C coupled methylene groups and 28 % of methyl groups as a result of reduction; only trace amounts of o-xylene and dimeric or trimeric coupling products, but no 2 at all could be detected by GC/MS (Table 1, entry 1)
These results agree rather well with those obtained by Alder under anhydrous conditions in DMF [6]
Summary
Introduction oQuinodimethanes (o-xylylenes) are reactive intermediates widely used for the synthesis of polycyclic compounds via inter- or intramolecular Diels-Alder reactions [1]. Recent progress in aqueous Diels-Alder cycloadditions and organometallic reactions [3], especially the successful Wurtz coupling of benzylic halides [4] and their Barbier addition to carbonyl compounds [5], prompted us to study the behaviour of α,α'-dihalo-o-xylenes (1) under similar conditions in the hope to obtain benzocyclobutene (2) or, in the presence of dienophiles, cycloadducts of o-quinodimethane.
Talk to us
Join us for a 30 min session where you can share your feedback and ask us any queries you have
Disclaimer: All third-party content on this website/platform is and will remain the property of their respective owners and is provided on "as is" basis without any warranties, express or implied. Use of third-party content does not indicate any affiliation, sponsorship with or endorsement by them. Any references to third-party content is to identify the corresponding services and shall be considered fair use under The CopyrightLaw.