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1‐Phenyl‐1,2‐cyclohexadiene: Generation, Interception by Activated Olefins, Dimerisation and Trimerisation
Author(s) -
Christl Manfred,
Schreck Michael,
Fischer Thomas,
Rudolph Marcus,
Moigno Damien,
Fischer Hartmut,
Deuerlein Stephan,
Stalke Dietmar
Publication year - 2009
Publication title -
chemistry – a european journal
Language(s) - English
Resource type - Journals
SCImago Journal Rank - 1.687
H-Index - 242
eISSN - 1521-3765
pISSN - 0947-6539
DOI - 10.1002/chem.200900717
Subject(s) - trimer , chemistry , dimer , furan , indene , medicinal chemistry , diradical , crystal structure , stereochemistry , organic chemistry , singlet state , physics , nuclear physics , excited state
Four possible precursors of 1‐phenyl‐1,2‐cyclohexadiene ( 2 ) were examined, namely, 6,6‐dibromo‐1‐phenylbicyclo[3.1.0]hexane, (1α,5α,6α)‐6‐bromo‐6‐fluoro‐1‐phenylbicyclo[3.1.0]hexane, 1‐bromo‐2‐phenylcyclohexene and 1‐bromo‐6‐phenylcyclohexene. All four compounds could be converted into 2 , as demonstrated by the products of the interception of 2 with activated olefins. Styrene, 1,1‐diphenylethene, indene, furan and 2,5‐dimethylfuran were employed as such. Whereas the first three gave [2+2] cycloadducts of 2 , the last two provided one [4+2] cycloadduct each. To create the [2+2] cycloadducts, the π bond of 2 that is more remote from the phenyl group reacted, whereas the π bond of 2 conjugated with the phenyl group exclusively produced the [4+2] cycloadducts. The generation of 2 in the absence of a trapping reagent brought about relatively good yields of a dimer or a trimer of 2 depending on the mode of the liberation of 2 . Being derivatives of triphenylene, the dimer as well as the trimer have unusual structures, thereby indicating that a phenyl group is participating in the formation of these compounds. The most surprising structure of the trimer was elucidated by X‐ray crystal diffraction. As to the mechanisms, diradical intermediates are proposed both for the cycloadditions and for the dimerisation. The initial steps of the latter seem to proceed also in the trimerisation.