Abstract
The reaction of (ortho-acetalaryl)arylmethanols with various phosphines PR(1)R(2)R(3) (R(1) = R(2) = R(3) = Ph; R(1) = R(2) = Ph, R(3) = Me and R(1) = R(2) = Me, R(3) = Ph) under acidic conditions (e.g., HCl, HBF(4), TsOH) unexpectedly led to the formation of (10-hydroxy-9,10-dihydroanthr-9-yl)phosphonium salts instead of the corresponding anthryl phosphonium salts. The cyclization occurred according to the Friedel-Crafts mechanism but without the usually observed Bradsher dehydration, giving cyclic products in the form of cis/trans isomers and their conformers. In case of electron-rich and less-hindered dimethylphenylphosphine, all four stereoisomers were recorded in (31)P{(1)H} NMR spectra, while for the other phosphines, only the two most stable cis/trans stereoisomers were detected. This study was supported by DFT and NCI calculations in combination with FT-IR analysis.