Solution-Spray Flash Vacuum Pyrolysis: A New Method for the Synthesis of Linear Poliynes with Odd Numbers of C≡C Bonds from Substituted 3,4-Dialkynyl-3-cyclobutene-l,2-diones

We report a new method for the preparation of a wide range of linear poliynes, 1a−1i, with an odd number of C≡C bonds. This method is based on solution-spray flash vacuum pyrolysis (SS-FVP) of the readily available 3,4-dialkynyl-3-cyclobutene-l,2-diones 3a−3i. It allows the synthesis of multigram quantities of a series of hexatriynes and decapentaynes from poorly volatile and thermally unstable precursors that cannot be subjected to conventional flash vacuum pyrolysis. Yields of the linear poliynes range from 42 to 99%. Similarly, the dodecahexayne 1j was obtained in 31% yield by SS-FVP of the bis(3-cyclobutene-l,2-dione) 3j. The synthesis of the new 3,4-dialkynyl-3-cyclobutene-l,2-diones 3h−3j via the ketals 7, 10, and 13 is reported. The X-ray crystal structure of l,10-diphenyl-l,3,5,7,9-decapentayne (1c) was solved, and the crystal packing structure provides valuable information to explain the thermal polymerization behavior observed for this compound in the crystalline state.