Herein we have developed the silver-catalyzed electronic- and steric-controlled intramolecular formal [2 + 2]-cycloaddition of alkyne-tethered cyclohexadienones. Substrates with electron-rich alkynes and a less hindered quaternary carbon center afford tricyclic… Click to show full abstract
Herein we have developed the silver-catalyzed electronic- and steric-controlled intramolecular formal [2 + 2]-cycloaddition of alkyne-tethered cyclohexadienones. Substrates with electron-rich alkynes and a less hindered quaternary carbon center afford tricyclic fused cyclobutenes through 1,7-enyne cyclization. In contrast, the formation of dihydrofurans was observed from electron-deficient alkynes via proton abstraction/C-O bond cleavage. The synthetic potential of this method was also broadened with a gram-scale reaction and various transformations on cyclobutene.
               
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