Protonation of Diarylacetylenes in Superacid HSO3F and Their Oxidation in the HSO3F/PbO2 System: One-Pot Synthesis of Polysubstituted Naphthalenes
In the superacid HSO3F, diarylacetylenes bearing one electron-withdrawing group (NO2, CN, COMe, CO2Me) in each arene ring form stable ions, protonated at these groups. Oxidation of such diarylacetylenes in the HSO3F/PbO2 system at –75 to –50 °C over 2–2.5 h, followed by quenching of the reaction mixture with hydrochloric (or hydrobromic) acid at –60 to 25 °C, resulted in the formation of (E,E)-1,4-dichloro (or dibromo)-1,2,3,4-tetraarylbuta-1,3-dienes. These butadienes spontaneously undergo electrocyclic transformation into polysubstituted naphthalenes at room temperature. (© Wiley-VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)