| Activation of carbon-carbon bonds by transition-metal catalysts has shown unique potentials in molecule reoganization,providing intriguing transformations and synthetic strategies that are otherwise difficult to achieve by traditional methods.Cyclobutanone compounds have been extensively studied due to their unique reactivity,in particular,catalytic ring expansion of cyclobutanones with unsaturated motifs provides efficient access to various cyclic scaffolds.Currently,the ring-expansion processes of cyclobutanone is mostly realized by oxidation addition and β-carbon elimination strategies,however,other catalytic ring-expansion processes have rarely been disclosed.Therefore,it is significant to explore other catalyst systems to apply them to the ring expansion reaction of cyclobutanone.In recent years,the stoichiometric amount of Lewis acids have been reported to promote ring-opening of cyclobutanones and realized alkyne-carbonyl metathesis using the Lewis acids as catalysts.Based on the above research,we have achieved the Sonogashira coupling reaction of o-bromoarylcyclobutanone and terminal alkynes to form a series of β-(2-ethynylphenyl)cyclobutanone compounds in moderate yields under mild conditions.A range of substrates decorated with various substituents were all well accommodated.Based on the above work,a ring-opening/alkyne-carbonyl metathesis sequence ofβ-(2-ethynylphenyl)cyclobutanones catalyzed by Ag is realized to furnish multisubstituted naphthyl ketones in good yields.The reaction proceeded on mild condition and has good functional group tolerance,as well performed on a gram scale.Besides,to demonstrate the efficacy of this method,it was applied in synthesis of the benz[a]anthracene-7,12-dione.To gain a better understanding of the mechanistic details,density functional theory(DFT)calculations were performed on the Ag-promoted ring-opening process.It indicated that the C-C bond cleavage process may be involved as a rate-determining step. |
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