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

Abstract

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 re-arrangement 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.

Keywords

• Dewar benzenes
• fluorenes
• rearrangement
• reduction
• fused-ring systems