No abstract

Rearrangement of aryl‐substituted Dewar benzenes into the corresponding biaryls may serve as an alternative pathway for synthesis of sterically hindered biaryls. The kinetic data obtained from thermal rearrangements of Dewar benzenes provide experimental evidence for the proposed orbital‐symmetry‐controlled electrocyclic ring opening. (© Wiley‐VCH Verlag GmbH & Co. KGaA, 69451 Weinheim, Germany, 2008)

No abstract

No abstract

The first Dewar benzene-ferrocene conjugates were synthesised by the reaction of tetraalkylcyclobutadiene-AlCl(3) complexes with 3-ferrocenylpropynoates. Owing to extensive delocalisation, these conjugates feature unusually high thermal and chemical stability, rearranging to their corresponding phenylferrocenes (benzenes) under forcing microwave irradiation conditions.

Tetramethylcyclobutadiene-AlCl 3 complex reacted with bisalkynes possessing phenylene and biphenylene spacer giving rise to mono-and bis-Dewar benzenes. The rearrangement of the bis-Dewar benzene derivatives under thermal conditions (150°C) yielded the corresponding linear ter-and quaterphenyl compounds possessing substituted terminal benzene rings. A mixture of an alkynylbiphenyl and a terphenyl was also obtained by the reaction of tetramethylzirconacyclopentadiene with bisalkynylbenzene in 13% combined yield.

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.

JANKOVA, S.; DRACINSKY, M.; CISAROVA, I.; KOTORA*, M.; Eur.