Dehydration of 4-hydroxy-2,3,4-triphenylcyclopent-2-enone

Abstract

Dehydration of the title alcohol with toluene p-sulphonic acid in benzene yields a yellow dimer identified as trans-2,2′-dioxo-3,3′,4,4′,5α,5′β-hexaphenyl-1,1′-bi(cyclopentenylidene)(IV). Irradiation in sunlight causes isomerisation about the central double bond and the cis-isomer obtained (IX) is thermally reconverted into the trans at 185°. A second dimer isolated from the same reaction is formulated as 2,3,3a,5,6-pentaphenyl-3a,3b,6a,10b-tetrahydrobenz[e]-as-indacene-1,4-dione (XIII). Dehydration of the title alcohol with acetic acid–sulphuric acid yields a blue dehydro-dimer, 3-hydroxy-1,2,5,6,10b-pentaphenyldihydrobenz[e]-as-indacen-4-one (XIV), whose allyl ether undergoes a Claisen rearrangement and an internal Diels–Alder addition. The mass spectra of two dimethoxylated analogues (XXIX) and (XXX) are discussed.