(±)-Polysiphenol and Other Analogues via Symmetrical Intermolecular Dimerizations: A Synthetic, Spectroscopic, Structural, and Computational Study
| Autor: | D. Christopher Braddock, Anna Duran-Corbera, Masih Nilforoushan, Ziye Yang, Tianyou He, Gajan Santhakumar, Karim A. Bahou, Henry S. Rzepa, Rudiger Woscholski, Andrew J. P. White |
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| Rok vydání: | 2022 |
| Předmět: | |
| Zdroj: | Journal of Natural Products. 85:2650-2655 |
| ISSN: | 1520-6025 0163-3864 |
| DOI: | 10.1021/acs.jnatprod.2c00749 |
| Popis: | We report an improved total synthesis of 4,5-dibromo-9,10-dihydrophenanthrene-2,3,6,7-tetraol, (±)-polysiphenol, via intermolecular McMurray dimerization of 5-bromovanillin and subsequent intramolecular oxidative coupling as the key steps. The synthetic route is applicable to 4,5-dichloro- and 4,5-difluoro-halologues (as well as a 4,5-dialkyl-analogue). Distinctive AA′BB′ multiplets in their 1H NMR spectra for the dimethylene bridges of the dibromo and dichloro compounds reveal them to be room-temperature stable atropisomers, while for the difluoro compound they present as a singlet. X-ray crystal structure determinations of their tetramethylated synthetic precursors show atropisomeric twist angles of 48°, 46°, and 32°, respectively, with the former representing the largest yet observed in any 4,5-disubstituted-9,10-dihydrophenanthrene. DFT computational studies reveal an unprecedented two-stage atropisomeric interconversion process involving time-independent asynchronous rotations of the dimethylene bridge and the biaryl axis for halologues containing chlorine or bromine, but a more synchronous rotation for the difluoro analogue. |
| Databáze: | OpenAIRE |
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