Benzofluorenones have be prepared by heating 1,2-diphenylethynylbenzenes in the presence of copper(I) catalyst. The yield of the benzofluorenone and the distribution of various other products formed appear to depend on the temperature of the reaction and the presence of adventitious water and oxygen. The proposed mechanism for the formation of the observed products involves a 5-exo-dig cyclization step that occurs either before or after the involvement of water. The transition states of the cyclization and the water incorporations were modeled using various DFT methods, and the relative barrier heights have been correlated to the dependence of the product yields on the concentration of water in the reaction mixture.

DFT modeling of the 5-exo-dig cyclization in the mechanism proposed for the cycloaromatization of ortho-diynylarenes

ACS Fall 2021

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