A Halogeno-derivatives

Halogeno-derivatives.—Interest in the reactivity of trichlorophos-phazenyl derivatives, RN=PCl3, which may exist as monomers or cyclic dimers, has been sustained. Previous findings on the reactivity of the dimers (18) to sulphur dioxide in polar solvents have been confirmed, and it is found that the cyclic dioxides (19) formed are readily cleaved by 

and mass spectroscopy showed that the N-H bonded compound was present, rather than its isomers, e.g. F2P(S)-N=Pp20H or HS-F2P=N P0F2. The A -deuteriated analogues, XX P(S)-ND-POF2, were obtained by solvolysis with deuteriated formic acid. 

Reactions of the same halogenophosphazenes with ammonia were also described, in which halide-ion displacement took place at the phosphazenyl group rather than at the thiophosphoryl group  

In one of the ammonolysis products, halide ion exchange occurred 2FCIP(S)-N=PF2NH2 

A related form of isomerization to that described above has been studied in the case of the esters (20) 

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In some ylides photolytic conditions were necessary for their transylidation [30]. The conversion of iodonium ylides into a-halogeno derivatives of the parent carbonyl compound (or other precursor) with hydrogen halides is normally effected directly, without isolation of their iodonium salts. A similar reaction with halogens leads to the formation of a,a-bis halogenated products [31]. The reaction of pyridines with the non-isolable PhI=C(CN)2 is of interest, since it permits the ready transfer of the C(CN)2 functionality to the nitrogen of pyridine, quinoline, etc. the yields here were generally moderate but in some cases the products could not be obtained using other dicyanocarbene precursors [32],... 

Cagniant et al.sl have extended to tellurophenes a method of synthesis, recently developed for thiophenes and selenophenes,33 34 based on the condensation of a /J-halovinyl aldehyde with sodium telluride and a halogeno derivative of general formula X—CH2—R [Eq. (2)]. Some mono and polycyclic derivatives of tellurophene have been prepared using the above procedure. 

In the 1,2,4-thiadiazole ring the electron density at the 5-position is markedly lower than at the 3-position, and this affects substituent reactions. 5-Halogeno derivatives, for example, approach the reactivity of 4-halogenopyrimidines. The 1,2,4-oxadiazole ring shows a similar difference between the 3- and 5-positions. 

The catalytic effect of protons has been noted on many occasions (cf. Section II,D,2,c) and autocatalysis frequently occurs when the nucleophile is not a strong base. Acid catalysis of reactions with water, alcohols, mercaptans, amines, or halide ions has been observed for halogeno derivatives of pyridine, pyrimidine (92), s-triazine (93), quinoline, and phthalazine as well as for many other ring systems and leaving groups. An interesting displacement is that of a 4-oxo group in the reaction of quinolines with thiophenols, which is made possible by the acid catalysis. 

The chemistry of thiazoles is interesting in view of their propensity for biological activity. Eor that reason thiazoloquinolines have also been a widely studied group of compounds. A preferred route to thiazoles exploits a-halogeno ketones in a reaction with thioamides to give the fused 2-substituted thiazole derivatives. 

Attempts to prepare selenazole derivatives were first described by Hofmann,2 a student of Hantzsch, in connection with investigations in the thiazole series. By reaction of selenobenzamide with a-halogeno compounds corresponding to the general reaction (2, R" = CeHg), he synthesized a series of 2-phenylselenazoles. In the same way, several... 

The Suzuki cross coupling reaction features in a synthesis of 4-arylcoumarins from the 4-halogeno derivatives c96JCS(Pl)2591> and in a route to the thieno[3,4-c]coumarin (8) from which coumarin 3,4-quinodimethane (9) can be thermally generated <96T3117>. 

Stereospecific dependencies of the nonselective relaxation-rates for other protons in a sugar molecule may be seen in the data for a set of 3,4,6-tri-O-acetyl-l-0-benzoyl-2-deoxy-2-bromo-D-hexopyranose derivatives (40-42), as well as other 2-halogeno derivatives. A comparison of their... 

Structures of type A result on protonation of monoalkyl-pentahydro-doso-hexaborate ions B6H5R2 while type B anions are observed for the halogeno derivatives [B6H5X]2 (X = Cl, Br, I) [78], This regiospecificity results from inductive... 

A large number halogenated cycloproparenes is known, in particular the 1,1 -di-halogeno derivatives, which are available by the cycloaddition approach mentioned above. The 2- and 3-halogenobenzocyclopropenes 202 and 204 are conveniently synthesized by the carbene addition route from the appropriate precursors 201 and 203, respectively. 

Halides are displaced by a variety of nucleophiles including alkoxides, phenoxides, thiolates, cyanide, and amines. 4-Halogenobenzofurazans yield either 4-or 5-substituted products resulting from normal ipso or cine reactions, and 5-halogeno derivatives react similarly. An addition lim-ination AE mechanism has been invoked to explain the cine products, whereas ipso substitution can result from both AE and Sj.,Ar pathways (Scheme 14) <81MI 405-02). 

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