Highly diastereoselective rhodium@) acetate-catalysed intramolecular addition of a-diazo ketones to aromatic rings to form the azulenones 3 has been achieved; the norcaradiene form of 3 undergoes efficient stereospecific cycloaddition with phenyltriazolinedione, in either a stepwise or a tandem process, leading to the pentacyclic systems 4 as a single diastereomer in each case.
A systematic investigation of the influence of substitution at positions C-2 and C-3 on the azulenone skeleton, based on NMR characterisation, is discussed with particular focus on the impact of the steric and electronic characteristics of substituents on the position of the norcaradiene-cycloheptatriene (NCD-CHT) equilibrium. Variable temperature (VT) NMR studies, undertaken to enable the resolution of signals for the equilibrating valence tautomers revealed, in addition, interesting shifts in the equilibrium.
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