Fluorous silyl group

Fluorous trialkyl silyl protecting groups have also been used to simplify the purification of complex reaction mixtures [5] (Scheme 3.16). Separation of the reaction products can be achieved by means of a simple three-phase extraction (aqueous/or-ganic/fluorous) instead of the usual chromatography. In this respect, the concept of using fluorous protecting groups has some parallels with the solid-phase-sup-ported chemistry which also was primarily developed to simplify multiple workup operations. 

Scheme 3.16 Simplification of product purification after 1,3-dipolar cycloaddition by use of fluorous silyl protecting groups (R — H, CH3 — CH3, C3H7, Ph) [5]. The nitrile oxide (R -CNO) is generated in situ by either the Huisgen or Mukaiyama method [6].

Biginelli reaction (Scheme 3.12) [64,67]. Excess (3-ketoester and aldehyde was separated from the fluorous reaction product by partitioning between toluene and FC-84 (mixture of isomers of C7Flft). The same system was used after cleavage of the silyl group with TBAF. In this case the toluene extracted the desired product while the fluorous silyl fluoride remained in the fluorous phase. 

Fluorous silyl ethers have also been developed to serve as protecting groups for carbohydrates. A light fluorous silicon group (2, Scheme 8.1) was wielded for the protection of a donor building block, and a trisaccharide was synthesized... 

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