One-step synthesis of 2,3-difluoronaphthalene by the gas-phase co-pyrolysis of styrene with chlorodifluoromethane

Abstract

The gas-phase co-pyrolysis of styrene with CHClF₂ in a flow reactor at 550–650 °C gives 2,3-difluoronaphthalene in two parallel reaction channels. The main channel includes decomposition of CHClF₂ to difluorocarbene, whose subsequent cycloaddition to styrene affords 1,1-difluoro-2-phenylcyclopropane. This compound rearranges to 2-fluoroindene giving finally difluoronaphthalene upon the second difluorocarbene cycloaddition and subsequent aromatization of the resulting cycloadduct. The second reaction channel consists in aromatization of 1,1,2,2-tetrafluoro-3-phenylcyclobutane, which is formed by the [2+2]-cycloaddition of styrene to tetrafluoroethylene, a product of difluorocarbene dimerization.