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The First Example of the Friedel–Crafts Cyclization Leading to (10-Hydroxy-9,10-dihydroanthr-9-yl)phosphonium Salts without the Expected Bradsher Dehydration
oleh: Krzysztof Owsianik, Ewa Różycka-Sokołowska, Marek Koprowski, Marika Turek, Łucja Knopik, Vivek Vivek, Bogdan Dudziński, Piotr Bałczewski
Format: | Article |
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Diterbitkan: | MDPI AG 2024-02-01 |
Deskripsi
The reaction of (<i>ortho-</i>acetalaryl)arylmethanols with various phosphines PR<sup>1</sup>R<sup>2</sup>R<sup>3</sup> (R<sup>1</sup> = R<sup>2</sup> = R<sup>3</sup> = Ph; R<sup>1</sup> = R<sup>2</sup> = Ph, R<sup>3</sup> = Me and R<sup>1</sup> = R<sup>2</sup> = Me, R<sup>3</sup> = Ph) under acidic conditions (e.g., HCl, HBF<sub>4</sub>, 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 <i>cis/trans</i> isomers and their conformers. In case of electron-rich and less-hindered dimethylphenylphosphine, all four stereoisomers were recorded in <sup>31</sup>P{<sup>1</sup>H} NMR spectra, while for the other phosphines, only the two most stable <i>cis</i>/<i>trans</i> stereoisomers were detected. This study was supported by DFT and NCI calculations in combination with FT-IR analysis.