Fluorous compounds Reagents

On the heels of work by Zhu and Horvath and Rabai, perfluorocarbon solvents and fluorous reagents have been used increasingly in organic syntheses. Ruorous compounds often partition preferentially into a fluorous phase in organic/fluorous liquid-liquid extraction, thus providing easy separation of the compounds. Tris[(2-perfluorohexyl)ethyl]tin hydride combines the favorable radical reaction chemistry of trialkyltin hydrides with the favorable separation features of fluorous compounds. 

Fluorous biphase reactions have been reviewed extensively in the past few years, and most important types of reaction may now be conducted under fluorous conditions [46,51], However, partitioning of catalysts and reagents into the fluorous phase is seldom perfect - even a loss of 1-2% of an expensive catalyst may be unacceptable. Solubility and partitioning between phases relies on a complex balance of properties and interactions, and rather than simply adding more fluorocarbon chains to a catalyst (which is a common approach to the problem of leaching of catalyst from the fluorous phase), studies have indicated that the partition coefficients of fluorous compounds may better be optimised by... 

The allylation of carbonyl compounds with allyltin reagents is still an active area of organotin chemistry from the methodological point of view, and also for synthetic applications. For completeness we should add several alternative techniques, such as the development of trifluoromethanesulphonic acid as a Bronsted acid catalyst for the allylation of aldehydes in water123, or the design of fluorous allyltin reagents for the platinum-catalysed allylation of aldehydes124. 

Fluorous compounds and solvents have emerged as powerful tools in modem synthetic organic chemistry. The concept of fluorous biphasic system and fluorous biphasic catalysis is based on catalysis through the use of reagents that have perfluorinated carbon chains. 

In 2004, Kumar and Montanari introduced a fluorous tagged trivalent iodonium compound that can be used as a tag for /-Boc based solid phase peptide synthesis by tagging free amines with a perfluoroheptyl (W-C7F15) group.It is an efficient fluorous tagging reagent that has the potential to help in the synthesis of both routine and difficult peptide and protein sequences. The... 

Carbonylation of fluorous compounds was also tested with the use of conventional tributyltin reagents. In this case the fluorous product is isolated from the fluorous media and conventional tin compounds are isolated from organic media. Unfortunately, the carbonylation of perfluoroalkyl radicals was unsuccessful, probably because of the very rapid reaction of these electrophilic radicals with allyltributyltin [56]. However, 2-(perfluoroalkyl)ethyl radical can be used for this radical carbonylation. In this case, FRPS separation again works well for the preparation of the product from tin compounds. 

Fluorous tin reagents. A gen ->elow. These compounds have su Ph,P)PdCl2 with LiCl as an additive... 

Fluorous tin reagents A general method for the syntheis of the reagents is shown below. These compounds have successfully been applied in Stille coupling using iPhjPfPdClj with LiCl as an additive in DMF-THF at 80°. 

The same strategy was applied to radical cabonylation with fluorous allyltin reagents. Propylene-spaced fluorous allyltin reagents 22 were tested as mediators for radical carbonylations the four-components coupling reaction with RX, CO, alkenes and the fluorous allyltin produced the -functionalized i8-aUylated ketones 23 (Scheme 28). Diphasic workup (acetonitrile and FC-72) was successfully carried out to separate the products from the tin compounds. Comparison experiments... 

Some of the disadvantages of the Stille reaction, e. g. the low reactivity of some substrates, separation difficulties in chromatography, and the toxicity of tin compounds, have been ameliorated by recent efforts to improve the procedure. Curran has, in a series of papers, reported the development of the concept of fluorous chemistry, in which the special solubility properties of perfluorinated or partly fluorinated reagents and solvents are put to good use [45]. In short, fluorinated solvents are well known for their insolubility in standard organic solvents or water. If a compound contains a sufficient number of fluorine atoms it will partition to the fluorous phase, if such a phase is present. An extraction procedure would thus give rise to a three-phase solution enabling ready separation of fluorinated from nonfluorinated compounds. 

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