Kinetic or Thermodynamic Product? Case Studies on the Formation of Regioisomers of Tetraphenyladamantanes
| Autor: | Clemens Richert, Wolfgang Frey, Tim Berking |
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| Rok vydání: | 2023 |
| Předmět: | |
| Zdroj: | Synthesis. |
| ISSN: | 1437-210X 0039-7881 |
| DOI: | 10.1055/a-2097-0092 |
| Popis: | Tetraaryldamantanes (TAAs) with alkoxyphenyl groups are interesting synthetic targets because they can act as crystallization chaperones for liquid compounds. Their carbon framework is set up by Friedel-Crafts alkylation, using adamantane-1,3,5,7-tetraol and anisole derivatives as starting materials. One successful chaperone is 1,3,5,7-tetrakis(2-bromo-4-methoxyphenyl)adamantane (TBro). This compound was initially considered the thermodynamic product of alkylation. We now report that exposure of TBro to strong Brønsted acid leads to its regioisomer 1,3,5,7-tetrakis(4-bromo-2-methoxyphenyl)adamantane (iTBro) as the dominant product, obtained in a yield of 68%, far surpassing the 20% yield reported earlier for TBro. We also investigated the reactions of 3-iodo-, 3-chloro-, and 3-fluoroanisole to the corresponding TAAs and obtained yields of 66%, 26% and 52% for the main regioisomer. While 3-iodoanisole gave the same regioisomer as bromoanisole, 3-chloroanisole gave complex mixtures and 3-fluoroanisole gave 1,3,5,7-tetrakis(2-fluoro-4-methoxyphenyl)-adamantane (TFM) in 52% yield as the main product. When mixtures of regioisomers were isomerized with an excess of triflic acid, the thermodynamic products were obtained in 76-91%. These results show how subtle effects govern the regioisomeric product distribution of aryladamantanes. They also help to make novel crystallization chaperones accessible in yields. |
| Databáze: | OpenAIRE |
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