Synthesis of Fluorinated Precursors

Perfluoroalkyl iodides CFjfCFzjJ are commercially available reactants useful for interesting chemistry, offering various functional products such as CFj(CF2),C2HJ, CF3(CF2),C H.—G, where G represents hydroxyl, amine, thio, thiocyanate, isocyanate, nitrile, carboxy, or Cp3(CF2)x CH=CH2, CF,(CF2),CHiCH=CH2. 

However, crystallization occurs when x 7 and such behavior is not required in the elastomers. Consequently, it is necessary to synthesize co-oligomers from various fluorinated monomers such as vinylidene fluoride (VDF), trifluoroethylene 

The scope of telomerization was outlined by Starks in 1974, and further developed by Gordon and Loftus. We recently reviewed such a reaction in which mechanisms and kinetics of radical and redox telomerizations were described. 

Interestingly, the (co)telomers used behave as further potential telogens for subsequent telomerizations, and all of them can be end-capped with ethylene (E). 

These co-iodinated cotelomers were functionalized into vinyl or allyl type olefins by two different two-step processes as follow  

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In accordance with the transition state model discussed above, tertiary allylic alcohols rearrange with Uttle stereoselectivity unless the substituents at the quaternary stereocenter differ substantially in size. For instance, virtually no selectivity was observed by Johnson in a synthesis of fluorinated precursors for polyolefin cydizations (Scheme 7.17) [38]. 

The precursor was prepared via a lengthy sequence involving the elaboration of a Reformatsky adduct. The cyclic product was obtained as a 1.2 1 mixture of cis and trans isomers.The presence of the fluorine atoms had no effect on the efficiency of the cyclisation reaction. A subsequent study [384] extended the range of cyclisations to include trifluoromethyl alkyl and alkenyl radicals (Eq. 157). Free radical cyclisation reactions therefore show considerable promise for the rational synthesis of fluorinated carbocycles. 

When heated above 170 C hcxafluoropropylene oxide (5) is a source of difluorocarbene thus, heating 5 in the presence of an alkene allows the synthesis of fluorinated cyclopropancs under neutral conditions.The less readily available tetrafluoroethylcnc oxide (6) is also a precursor of difluorocarbene. ... 

Whereas in A-ethyl and A-methylaniline methoxylation occurs only on the methyl groups in the fluoromethyl substituted compounds, the regioselectivity is drastically changed. The a-methoxylated fluoroalkylamine have been used as precursors for the synthesis of fluorinated amino acids and dihydroquinolines [272]. 

This chapter is a continuation from Part I of this review of fluorine-containing heterocycles recently published (03AHC(86)129). Part II deals with the synthesis of fluorine-containing heterocycles by condensations of two or more precursors. Major attention is paid to the use of mono- and 1,3-dicarbonyl substrates, and their nitrogen analogs. 

The synthesis of fluorinated, volatile bismuth )3-diketonates for MOCVD was reported in a recent submission by Sievers et al. [243]. Bi(fod),i was isolated and characterized to be sufficiently volatile for CVD growth of bismuth films although no BSCCO film growth has yet been demonstrated. This report also provides an excellent survey of volatile bismuth metal-organic and organometallic precursor chemistry. 

Another possibility for the synthesis of fluorinated pyrroles is the use of their nonaromatic precursors. Thus, 3,3-difluoro-l-pyrrolines 30 were prepared via electrophilic fluorination of the corresponding 1-pyrrolines 29 by Selectfluor. Reaction of the difluoropyrrolines 30 with sodium aUcoxides yielded fluorinated 5-(alkoxymethyl) pyrroles 31 in good yields [18],... 

Fluorinated pyrroles have been studied intensively in recent years. As a resnlt, a significant number of synthetic approaches to these compounds was elaborated. The most general methods involve direct fluorination/trifluoromethylation of the parent pyrroles, both the [3 -1- 2]- and the [4H-2]-cycloaddition reactions, the applications of carbonyl compounds as well as TOSMIC and isocyanoacetates. Thongh variety of methods are already known, the elaboration of novel preparative pathways towards fluorinated pyrrole derivatives is still ongoing, which is due to the manifold of biological activities of this structural motive and the use as precursors for porphyrins synthesis. It is no doubt, that this branch of synthetic organic chemistry will enjoy a much attention, giving rise to sustainable flow of novel convenient pathways to the synthesis of fluorinated pyrroles. 

The synthesis of fluorinated oxadiazoles can be achieved from open-chain flnorinated precursors through conventional heterocyclization reactions such as the amidoxime route (i in Scheme 1) and the cycloaddition route (ii in Schane 1), both necessitating of a nitrile precursor [7]. 

Scheme 35 Synthesis of fluorinated 1,2,4-thiadiazole from fluorinated acyclic precursors...

Scheme 47 Synthesis of fluorinated 1,2,5-thiadiazole by direct introduction of fluorine on the ring through nucleophilic substitution or starting from fluorinated acyclic precursors...

The reaction of bromo or chloro derivatives of triazines with the fluoride ion is one of the main methods for the synthesis of fluorinated 1,2,4-triazines [13]. For instance, l,3-dimetyl-5-fluQro-6-azauiacyl 16 was obtained by reacting dry potassium fluoride with the corresponding bromo precursor 15 (Scheme 11) [19]. 

Simple and Complex Organic Molecules. Using modem direct fluorination technology, the synthesis of even the most complex perfluorocarbon stmctures from hydrocarbon precursors is now possible. For example, syntheses of the first perfluoro crown ethers, perfluoro 18-crown-6, perfluoro 15-crown-5, and perfluoro 12-crown-4 (54) have been reported. Perfluoro crown ethers (54,55) are becoming important as the molecules of choice for many F-nmr imaging appHcations (56) in humans and are particularly effective in brain and spinal diagnostics when... 

Perfluoroalkyl)ethane thiols have been used as precursors to fluorinated surfactants and products for hydro- and oligophobic finishing of substrates such as textiles and leather (1). The synthesis of 2-(perfluoroalkyl)ethane thiol and a byproduct bis-(-2-perfluoroalkylethane)-disulfide (5-10%) has been practiced via the reaction of 2-(perfluoroalkyl)ethane iodide with thiourea to form an isothiuronium salt which is cleaved with alkali or high molecular weight amine as shown in Equation 1 for 2-(perfluorohexyl)ethane iodide (1). 

A potentially useful variant of the synthesis of some Mo(CHR)(NAr)(OR )2 complexes (R=CMe3 or CMe2Ph) consists of addition of two equivalents of a relatively acidic alcohol (R OH=a fluorinated alcohol or phenol) to Mo(NAr)(N-t-Bu)(CH2R)2 [78,79], a variation of the reaction of that type that was first reported in 1989 [80]. The more basic t-butylimido ligand is protonated selectively. This synthesis avoids the addition of triflic acid to Mo(NAr)2(CH2R)2 to give Mo(CHR)(N-t-Bu)(triflate)2(dimethoxyethane), the universal precursor to any Mo(CHR)(NAr)(OR )2 complex. Unfortunately, the method does not appear to succeed when R OH does not have a relatively high pK,. 

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