Organic compounds -- part of the class 532-570 series – Organic compounds – Carbohydrates or derivatives
Patent
1996-04-25
1998-08-04
Kight, John
Organic compounds -- part of the class 532-570 series
Organic compounds
Carbohydrates or derivatives
536 184, 536122, 570161, 570164, 570165, 570252, 570253, C07H 100, C07B 3900, C07C 17093
Patent
active
057895805
DESCRIPTION:
BRIEF SUMMARY
FIELD OF THE INVENTION
The present invention relates to selectively fluorinated organic compounds and their preparation.
BACKGROUND AND SUMMARY OF THE INVENTION
The selective fluorination of organic molecules has received considerable attention because of the profound effect that fluorine can have on the physical, chemical and biological properties of a wide range of substrates. For example, the introduction of a difluoromethylene unit into a molecule is an important target since the CF.sub.2 group is isopolar and isosteric with an ether oxygen and has a steric profile not dramatically different to that of a methylene group. Consequently, effective methods for constructing fluorine containing groups such as fluoromethyl, difluoromethylene or trifluoromethyl from readily available, cheap fluorinating agents are highly desirable and many reagents have been developed in order meet these targets.
DETAILED DESCRIPTION OF THE INVENTION
The fluorination of sulfur containing substrates offers an attractive route to fluoromethyl, difluoromethylene or trifluoromethyl containing substrates as many sulfur containing organic compounds are readily available from inexpensive starting materials by well established chemistry. Several methods for the fluorodesulfurization of organic compounds have been devised.
These reactions are generally performed by reacting the appropriate sulfur containing substrate with a combination of a source of electrophilic halogen such as N-bromosuccinimide with a fluoride ion donor such as pyridinium poly(hydrogen fluoride). Thus, fluoromethyl containing substrates may be prepared by treating a phenyl thioglycoside with diethylaminosufur trifluoride and N-bromosuccinimide. Difluoromethylene containing substrates may be prepared by reacting a 1,3-dithiolane with N-bromosuccinimide and pyridinium poly(hydrogen fluoride) or upon reaction with difluoroiodobenzene. Trifluoromethyl containing substrates may be prepared by treating an orthothio ester with N-bromosuccinimide and pyridinium poly(hydrogen fluoride). However, many of these reagents suffer from the disadvantages of being difficult to handle, they may be highly toxic and may be expensive.
The fluorination of thiocarbonyl containing substrates offers an attractive route to gem-difluoromethylene compounds as such substrates can readily be prepared from aldehydes or ketones by well established routes.
Only a few methods for the fluorodesulfurization of thiocarbonyl containing substrates are known. These typically involve the synthesis of .alpha.,.alpha.-difluoroethers from thioesters upon reaction with diethylaminosulfur trifluoride (DAST) or with bromine trifluoride. No extension of these methods to other thiocarbonyl derivatives has been proposed and, in addition, the reagents used are toxic, are difficult to handle and may be expensive.
According to the present invention there is provided a process for the preparation of a selectively fluorinated organic compound, which process includes the reaction of a precursor of the said organic compound, the precursor containing at least one group VI element selected from sulfur, selenium and tellurium, with a fluorinating agent and another halogenating agent and characterised in that the fluorinating agent is elemental fluorine.
The group VI containing precursor may be a thiocarbonyl containing substrate.
The group VI containing precursor may be contained in an inert solvent.
Preferably, the inert solvent may be a neutral substance such as acetonitrile and desirably may be a polar solvent such as dichloromethane or chloroform or an acid such as sulfuric acid or trifluoroacetic acid.
The halogenating agent may comprise elemental iodine or bromine or an interhalogen compound. The interhalogen compound may comprise iodine monochloride or iodine monobromide.
The process according to the present invention may be carried out by passing fluorine gas into the group VI containing precursor in solution in a suitable vessel. Alternatively, a flowing stream of the solution may be contacted with a gaseous
REFERENCES:
Monosaccharides: Their Chemistry and Their Roles in Natural Products, Ed. by Collins & Ferrier, (John Wiley & Sons, Ltd.: West Sussex, England), pp. 97-100, (1995).
Roush et al., J. Org. Chem., vol. 56:1649-1655, (1991).
Nicolaou et al., J. Amer. Chem. Soc., vol. 106:4189-4192, (1984).
Chambers Richard Dickinson
Sandford Graham
British Nuclear Fuels PLC
Kight John
Lee Howard C.
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