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Synthesis of 1,2,3,4-Tetramethyl- and 1,2,3,4-Tetraethylfluorene through a Dewar Benzene Pathway



A simple and selective synthesis of 1,2,3,4-tetra(m)ethylfluorenones and -fluorenes was achieved by using Dewar benzenes as important intermediates. The corresponding Dewar benzenes were prepared by reactions of tetraalkylcyclobutadiene–AlCl3 complexes with methyl phenylpropynoate. Their subsequent hydrolysis followed by photochemical rearrangement provided substituted biphenylcarboxylic acids. Treatment of the prepared acids with thionyl chloride gave rise to the fluorenones, which were reduced to the respective fluorenes. A Ru complex with 1,2,3,4-tetraethylfluorenone was prepared.

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