Isoxazolines, fluorous-tagged

The use of a triphasic extraction system, where an organic solvent, an aqueous phase and FC-72 [163] were used, allowed after any reaction step the isolation of the pure intermediates and eventually of the clean reaction products. The switch caused by the fluorous tag allowed the total partition of the library intermediates in the fluorous phase, where any other component of the reaction mixture was not dissolved, while after final deprotection the products were cleanly recovered from the organic phase and the tag moiety remained trapped by the fluorous phase. The eight isoxazoline alcohols were recovered with extremely high GC purities (> 91 %, average > 95%) and with moderate to good yields (from 29% to 99%). The low yields were probably due to the volatility of some of the final products. 

The same technique was also applied to the synthesis of a 10 member Ugi 4CC-derived solution library, where the fluorous tag was embedded into the carboxylic acid structure. The synthesis of the tag and the library synthetic scheme is shown in Figure 7.22. The tag was derived from a bromosilyl perfluorinated compound (C10F21CH2CH2, rather than C6Fi3CFI2CF[2, as for the isoxazolines) reacted with an orthothiobenzoate [164] and further elaborated with trivial chemistry. The library was produced using classical Ugi 4CC conditions and the tag detachment was obtained via treatment with... 

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