B synthesis

There are four main general methods [40 2] for the preparation of perfluorinated alkenes, namely dehydrohalogenation, dehalogenation, pyrolysis and halogen exchange reactions of appropriate fluorinated precursors. The overall features of the mechanisms of each of these processes have already been discussed (Chapters 6 and 7, Sections 1 and 11). Representative examples of each of these types of synthesis are collated in Table 7.5 clearly the method of choice for the synthesis of a particular fluoroalkene will depend 

Decarboxylation of fluoro-acids which, in turn, are prepared by electrochemical fluorination (ECF) on the industrial scale, is a useful route to longer-chain terminal 

Perfluorocyclopentene is exceptional in being obtained from non-fluorinated materials by a simple one-step procedure, i.e. displacement of chlorine in perchlorocyclopentene by fluoride ion [51], although some polyfluorochloro- and polyfluorohydro-alkenes can be made by analogous processes [51, 52]. If a perfluorocarbon is used as the reaction medium with potassium fluoride/18-crown-6 complex, then a variety of products may be obtained, including hexafluoro-2-butyne [53]. 

Many useful, higher-molecular-weight fluoroalkenes can be conveniently prepared by fluoride-ion-induced oligomerisation reactions of smaller fluoroalkenes such as tetrafluoroethene and hexafluoropropene, and these methods are discussed in Section C. 

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The photolysis of azirines has been shown to result in dimerization to pyrazines (72JA1395) and although this formally corresponds to a type B synthesis it involves an isolable intermediate (105) and does not proceed by simple dimerization (Scheme 70). 

The creation of the N—N bond as the last step of the ring synthesis is common in indazoles and very rare in pyrazoles. In indazoles this method is well known (type B synthesis (67HC(22)l), for example, the dehydration of oximes (570) with acetic anhydride yields 1-acetylindazoles (571), and in basic medium the indazole 1-oxides (573) are formed from the nitro derivatives (572). 

B. Synthesis by Annulation of the Pyrimidine Ring ONTO A 1,2,4-Triazole Structure... 

B. Synthesis of 1,2,4-Triazine 4-Oxides by Cyclization Involving NiU oso (Isonitroso)... 

Fig. 97. Temperature dependence of SHG signals normalized by signal of powdered LiNbO (hJhm LiNbOfl. Curves a and b - synthesis of Li4NbC>4F by in situ interaction between LifZOs and NbC>2F curve c and d — Li4Nb04F after holding at 800 and 1100°C, respectively curve e - LijNb04 synthesized at 600°C. Reproduced from [419], S. Y. Stefanovich, B. A. Strukov, A. P. Leonov, A. I. Agulyansky, V. T. Kalinnikov, Jap. J. Appl. Phys., 24 (1985) 630, Copyright 1985, with permission of Institute of Pure and Applied Physics, Tokyo, Japan.

Based on the successful series of transformations summarized in Scheme 1, Schreiber and Santini developed an efficient and elegant synthesis of periplanone B (1),8 the potent sex pheromone of the American cockroach, Periplaneta americana. This work constitutes the second total synthesis of periplanone B, and it was reported approximately five years after the landmark periplanone B synthesis by W.C. Still9 (see Chapter 13). As in the first synthesis by Still, Schreiber s approach to periplanone B takes full advantage of the facility with which functionalized 5-cyclodecen-l-one systems can be constructed via anionic oxy-Cope rearrangements of readily available divinylcyclohexanols.5 7 In addition, both syntheses of periplanone B masterfully use the conformational preferences of cyclo-decanoid frameworks to control the stereo- and regiochemical course of reactions carried out on the periphery of such ring systems.10... 

Ameduri, B. and Boutevin, B. Synthesis and Properties of Fluorinated Telechelic Monodis-persed Compounds. Vol. 102, pp. 133-170. 

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