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Chemoselectivity in the microwave-assisted solvent-free solid-liquid phase benzylation of phenols: O- versus C-alkylation |
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| Authors: | Gyö rgy Keglevich,Erika Bá lint,Alajos Grü n,Istvá n Greiner |
| Affiliation: | a Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, H-1521 Budapest, Hungary b Bálint Analytics, H-1116 Budapest, Fehérvári Street 144, Hungary c Research Group of the Hungarian Academy of Sciences at the Department of Organic Chemistry and Technology, Budapest University of Technology and Economics, H-1521 Budapest, Hungary d Gedeon Richter Plc., H-1475 Budapest, Hungary |
| Abstract: | The outcome of the solvent-free benzylation of phenol and 4-substituted phenols (such as 4-cresol and 4-chlorophenol) under MW irradiation was found to depend on the absence or presence of the base (K2CO3) and catalyst (triethylbenzylammonium chloride (TEBAC)). Reaction of benzyl halides at 80-120 °C in the presence of K2CO3 and TEBAC resulted in O-alkylation in high (89-96%) chemoselectivities. In the absence of TEBAC, the proportion of C-alkylation was considerable (16-34%). Omitting also K2CO3 from the reaction mixture, C-alkylation became predominant. In the case of 4-tert-butylphenol, the presence of TEBAC promoted C-alkylation. The selectivity of the alkylations can be fine-tuned by choosing the appropriate conditions. |
| Keywords: | Microwave heating Phase transfer catalysis Alkylation Selectivity |
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