Introduction

Technological progress in many respects is determined by quality of applied materials. The most perspective way to give necessary and sometimes predictable properties to materials is modification of an organic molecule by means of introduction of elements differed from hydrogen into it. Just so new materials have been created for recent years. Thus, a replacement of hydrogen atoms with fluorine leads to new unusual properties of all the molecule as a whole, that allows to consider organofluorine compounds as new sources of potentially interesting and important materials for new branches of technology [1-4]. If earlier such compounds found an application as models to solve some theoretical questions of organic chemistry, at present a great interest in practical implementation of these new materials have been outlined that caused by requirements of medicine and technique. Their production is possible in the following ways: at first, by direct fluorine insertion into organic molecules that stimulates development of new ways to the realization of the fluorination process itself. Second, insertion of fragments containing fluorine atoms into organic molecules that is the most attractive and encouraging strategy in construction of new molecules with a set of predictable properties; third, formation of an organic molecule of several fragments containing the fluorine atoms [5]. Transformations in changes of physical and chemical properties caused by the introduction of the fluorine atoms into different parts of a molecule are very specific and are not found in many cases in organic derivatives of different elements. Just singularity, originality sometimes, of the new materials promotes development of new technologies and approaches in organic synthesis and makes prospects for the use of organofluorine compounds as new materials in an expanded area of application. The introduction of the fluorine atoms into an aromatic ring is an important task for the organic and pharmaceutical chemistry. The known methods to introduce fluorine into the aromatic ring are rigidly limited by the classic Balts-Schiemann reaction and decarboxylation of fluoroformates . The direct fluorination of organic molecules with elemental fluorine, characterized by explosive behavior and caused by high exothermicity of the process, requires special conditions. Fluorine is an extremely active gas with the dissociation energy of the F-F bond of 37 kcal/mol and is able to enter very different reactions. The use of low temperatures, dilution of fluorine with inert gas or carrying out the process in inert solvent allow in many cases to "tame" fluorine activity. Serious difficulties in synthesis of organofluoric compounds with elemental fluorine called into being various versions of fluorine introduction into organic molecules by means of fluorine "carriers". They are substances that possess a reduced oxidizing ability and allow carrying out fluorination processes under controlled conditions. In recent years a certain progress in development of routes to introduce one or two fluorine atoms into the benzene ring was outlined. These methods are based on electrochemical fluorination in melts of salts of metal fluorides or in anhydrous hydrogen fluoride [5]. But these methods have significant disadvantages that are determined in main by a low selectivity of the process of replacement of hydrogen atoms of the benzene ring because it is accompanied by addition to multiple bonds. As regards unsaturated organic substances, the situation is more complicated because all methods are not selective and a substantial destruction of an organic substrate molecule takes place. That was obviously became apparent in attempts of selective introduction of fluorine atoms into steroids, sugars and other natural substances. Therefore the task is not only to "tame" active fluorine possessing high oxidizing properties but also to develop new technologies of the fluorination process itself that include both creation of a selective fluorinating agent and make the fluorination process easier. Though the use of higher fluorides of transition metals and hydrogen fluoride made possible in a number of cases to introduce the fluorine atoms into organic molecules, the well-known experimental difficulties and complexity of the process itself, plurality of fluorination routes did not permit to use the process in fine organic synthesis, although a substantial successes of the method have been acknowledged in producing series of freons and other fluorohalogen-containing compounds [6]. The exchange reactions of chlorine atoms with fluorine under subjection to fluorides of alkaline metals are effective only for systems containing strong electron-seeking groups; it substantially constricts the frames of application of this method. Xenon fluorides possess universal fluorinating ability. But availability of the fluorinating agent, ecological compatibility and range of application did not find proper development due to the presence of foully highly explosive admixtures in xenon difluoride and intensity of the fluorination. Systems that have the fluorine atom, bound with a heteroatom, oxygen, nitrogen and sulfur, seem more perspective. Even the first steps in this direction have shown availability to use this route. In fact, monographs [5-9] and reviews [10-14] have displayed the examples of high-selective fluorinating reagents based on compounds containing the oxygen-fluorine bonds. There is direct evidence of progress in realization of these routes, especially in fluorination of heterocyclic compounds, steroids, sugars and natural substances. After the pioneer work of Barton et al. [15,16] on reactions of fluorooxytrifluoromethane with organic substrates the number of examples of synthesis of fluorine organic compounds with the use of compounds, containing a O-F bond, increases continuously; their application in fine organic synthesis is not exotic now but it is a recognized process realized in industry. It may be affirmed that there is a tendency in revision of the concept of the elemental fluorine use in fluorination processes and in application of a number organic compounds containing the active fluorine atom at a heteroatom and it is possible to replace elemental fluorine as a reagent, though its important role as a system and fluorine source have been remained.

Though the reagents containing O-F bonds have been used for many years, only in recent years they found active application in the fluorination processes. Such reagents have attracted a great interest of chemists [8,10]. In spite of their usually high activity and moderate stability, they are found to be useful reagents in organic synthesis. More over, thanks to the work of prof. Rozen's team, new opportunities to use these compounds not only as fluorinating agents but also as unique oxidizers appeared; that made possible to carry out a number of important (from practical standpoint) processes to produce epoxides, to oxidize olefins etc. [10,17].

A recent synthesis of novel unique reagents of fluorooxytrifluoromethane, CF₃OF, and cesium fluorooxysulfate, CsSO₃OF, has been an event in this field that determined an increased interest of experts. Probably, for the first time researchers have on hand fluorooxy-reagents that could be isolated and used in individual state- in difference to majority of other fluorinating O-F reagents used as a rule in situ. These works initiate an extensive scope of investigations on the structure, reactivity and properties of compounds containing labile fluorine atoms at a heteroatom. They were aimed at development of a theory and methods of a synthesis of materials of new generation with attention to problems of technique, medicine and agriculture.

CF₃OF and CsSO₄F, which gave a powerful incentive to the development of researches, however have not been developed on an industrial scale due to a high cost and hence commercial impracticability of CF₃OF and due to insufficient safety in handling of CsSO₄F because of its ability to spontaneous at once decomposition (as a weak explosion, "clap") and is produced in small amounts only at the place of its use, in laboratories.

That is, in addition, one of the reasons that in daily practice the O-F-derivatives as fluorinating reagents yield to N-F-amines, stable compounds available in great variety and produced on an industrial scale.

In this review we have made an attempt to summarize and systemize new data on synthesis of fluorine organic compounds and a number of processes with the use of reagents containing O-F bonds. The main attention was paid to the comparative characteristics of these reagents, comparison of their opportunities with the fluorinating agents already in use and to reactions of the reagents containing O-F bonds with unsaturated compounds, heterocyclic and hetero-organic compounds. We do not examine OF₂ as a reagent for the fluorination because it, the same as fluorine, is difficult and dangerous to store and it is not so available in addition. Moreover, different peroxides containing the O-F bond, for example CF₃OOF etc., also were not included in our task.