Fluorous bipyridine

A similar reaction has been conducted under fluorous biphasic conditions, using a perfluoroalkylated bipyridine as ligand to ensure that the copper species resides in the fluorous phase [22], The oxidation of a range of primary alcohols to the corresponding aldehydes was found to be possible, an example of which is shown in Scheme 9.11. The catalyst could be successfully recycled by phase separation, with analytically pure products being isolated even after... 

Finally, two interesting systems with nonconventional solvents were reported. One uses the ionic liquid 1-butyl-3-imidazolium tetrafluoroborate ([BMIM][BF4]), giving results quite similar to those in CH2C12 with a large excess of pyridine, with good conversion and selectivity for the diepoxide (entry 8) [61]. The other nonconventional solvent used is the fluorous solvent hexafluoro-isopropanol. In the presence of 2,2 -bipyridine, this system gives full conversion and selectivity at a very low catalyst loading of 0.1 mol% (entry 9) [62],... 

The use of Cu in combination with TEMPO also affords an attractive catalyst [200, 201]. The original system however operates in DMF as solvent and is only active for activated alcohols. Knochel et al. [202] showed that CuBr.Me2S with perfluoroalkyl substituted bipyridine as the ligand and TEMPO as cocatalyst was capable of oxidizing a large variety of primary and secondary alcohols in a fluorous biphasic system of chlorobenzene and perfluorooctane (see Fig. 4.69). In the second example Ansari and Gree [203] showed that the combination of CuCl and TEMPO can be used as a catalyst in l-butyl-3-methylimidazolium hexafluorophosphate, an ionic liquid, as the solvent. However in this case turnover frequencies were still rather low even for benzylic alcohol (around 1.3 h 1). 

The Sonogashira coupling reaction of terminal alkynes with aryl or vinyl halides is a useful tool for carbon—carbon bond formation, and has found wide employment in areas such as natural product synthesis, the pharmaceutical industry, and material sciences. Novel recyclable Pd catalysts with fluorous ponytails in the ligand 2,2 -bipyridine were reported in a copper-free Pd-catalyzed Sonogashira reaction in a fluorous biphasic system (FBS) (Equation 4.19). The catalysts are only soluble in perfluorinated solvents at room temperature [41],... 

Recently, Betzemeier et al. showed that the scope of the copper-catalyzed oxidation reaction could be improved by using Cu Br Me2S instead of Cu Cl 97). The coordination of a perfluoroalkylated bipyridine to the metal centre produced a catalyst which could be used under biphasic fluorous conditions. Typically, 40)imol of perfluoroalkylated bipyridine was dissolved in 2mL of perfluorooctane. Next, 40 pmol of Cu Br Me2S was added, followed by a solution of 2 mmol alcohol and 64 imol TEMPO in 2mL chlorobenzene. The resulting biphasic reaction mixture was heated to 90°C under dioxygen (Fig. 27). 

---