Halogeno-derivatives

Halogeno-derivatives.—Anhydrous formic acid generally converts chlorophos-phazenes into phosphinyl compounds, and the reaction with Cl3P=NP(0)Cla is no exception  

A surprising feature of this product is that it does not readily eliminate hydrogen chloride (see also ref. 10), and can be converted into the iV-methyl analogue on reaction with diazomethane. These results may be contrasted with those observed for related compounds with P-alkyl substituents  

Acidolysis can, however, be re-directed to the phosphazenyl-phosphorus atom when Aik is CHClg or CCI3. 

spectra of Cl3P=NP(0)Cl2 and its N-labeIled analogue have been studied, and compared with the spectra of the [Cl8P NiiiPCl3] anion. C1 n.q.r. spectroscopy played an important role in enabling isomers (17) 

The JV-chloroethylphosphazene CCl3CCl2N=PCl3 generally undergoes reactions with aromatic amines at both phosphorus and a-carbon atoms  

Halogeno-derivatives.—jV-Chloroalkylphosphazenes undergo reactions with tri-cyanomethylsodium at the carbon, rather than at the phosphorus atom 53 

Other chloroalkylphosphazenes undergo thermal decomposition to give isocyanates,54 and not a mixture of isomers as previously reported  

The mass spectra of trichlorophosphazenes C13P—NX (X = sulphamoyl, acyl, aryl, or alkyl) and cyclodiphosphazanes (C13PNX) (X = alkyl) have been described in detail.58 

The energies of absorptions observed in the u.v. spectra of the phosphazenes R13P=NCR2=C(CN)2 (R1 = Ph, R2 = H, Cl, or CC13 R1 = Cl, R2 = Cl or CC13) have been compared with energies obtained from molecular orbital calculations.64 

Halogeno-derivatives.—JV-Halogenoalkyl-phosphazenes (35) have been convert-g(j33,34 aziridinyl derivatives (36) all phosphorus-halogen bonds are 

Alcoholysis of Cl3P=N—P(0)Cl2 gives bis(dialkoxyphosphinyl)amines (37), rather than alkoxyphosphazenes. At present, it is not clear whether this conflicts with the work of another group, who have found that the products of this type of reaction exist as a tautomeric equilibrium mixture involving the phosphazene (38) and the amide (39). 

The rates of reorientation of PCI 3 and of CCI3 groups of Cl3P=N—P(0)(CCl3)a in the solid state have been measured by Q n.q.r. spectroscopy. 

Halogeno-derivatives.—A new general method has been described for the selective halogenation of the methyl group of methyl ketones, based on treatment of the ethanolamine-derived ketimine (168) with either A-chloro-or iV-bromo-succinimide in ether, followed by mild acid hydrolysis presumably the tautomeric enamine (169) is the reactive species. 

Acid-catalysed bromination of methyl ketones in methanol constitutes an excellent method for the obtention of bromomethyl ketones the addition of small amounts of methanol to other solvents, such as ether or carbon tetrachloride, leads to results comparable to those observed in methanol alone. The directive effect of methanol is ascribed by the French authors to its intervention as a base in the reaction. 

Whereas electrochemical dimerization of crotonaldehyde gives the glycol (172), 3-methylcrotonaldehyde gives the lactol (173) as major product, severely limiting the generality of this method of dimerization.  

The products of methanolysis and ethanolysis of a range of A-phosphino-thioyl-phosphazenes, X 2P(S) N=PX 2C1 (X and X include Cl and F), have since been shown to have analogous structures. The solvolysis of F2P(S) N=PF2C1 by carboxylic acids may occur in different ways, depending on the nature of the acid employed  

and mass spectrometry show that the alcoholysis of A-sulphonyl-phosphazenes also occurs at the phosphazenyl group  

By comparison of these and other reactions with water and silylamines, it was shown that the reactivity to nucleophilic attack at a phosphazenyl phosphorus atom generally decreased in the order  

The reactions of sodium t-butyl peroxide with AT-sulphonylmonochloro-phosphazenes follow the expected course  

However, phosphoramides were obtained in reactions with analogous dichlorophosphazenes, probably as a result of the presence of traces of water in the reaction mixture  

Hexachloroacetone acts as a source of positive chlorine on reaction with enamines, furnishing, after acid hydrolysis, good yields of a-chloro-ketones. Thus the regioselectivity of enamine formation dictates the regioselectivity of chlorination.Similarly, cyclic enamines react with N2F2 to give the a-fluorocyclo-alkanone after hydrolysis.  

A full account concerning the regiospecific bromination of ketones using the halogen in the presence of 1,2-epoxycyclohexane has been published.  

Mercury(li) fluoride is recommended for achieving fluorine-bromine exchange in a-bromo-ketones.  

The methods of synthesis, properties, and reactions of j8-chloro-a/3-unsaturated aldehydes have been reviewed.In a recent innovation 8-chloro-a 8-unsaturated aldehydes are available through Vilsmeier formylation of ketones.  

Dicobalt octacarbonyl catalyses the hydrodebromination of bromomethyl ketones using a two-phase (benzene-NaOH) solvent system and a phase transfer catalyst. The 1,4-dione is formed as a side-product in some cases.  

The trimethylsilyl enol ether of an aldehyde or a ketone reacts with bromine to give the corresponding a-bromo-carbonyl compound since the enol ethers can be generated with a high degree of regioselectivity, this method of bromination is most 

The same salt, in the presence of peroxide, quantitatively brominates the a-position of /S-keto-esters a-bromination of cyclohexanone occurs in lower yield under the same conditions.  

Sulphuryl chlorofluoride (FSO2CI) gives 2-chlorocycIohex-2-enones on reaction with the parent cyclohexenone in liquid sulphur dioxide. 

A wide range of a-halogenoketones have been shown to be hydrodehalogenated by vanadium(ii) chloride.  

Inukai, H. Iwamoto, T. Tamura, I. Yanagisawa, Y. Ishii, and M. Murakami, Chem. and Pharnt. Bull. (Japan), 1976, 24, 820. 

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Nucleophilic substitution of benzene itself is not possible but the halogeno derivatives undergo nucleophilic displacement or elimination reactions (see arynes). Substituents located in the 1,2 positions are called ortho- 1,3 meta- and 1,4 para-. 

Triazoles are brominated at the 4- or 5-positions, but only if there is no Af-substituent <74AHC(16)33). This also applies to 1,2,4-triazoles. Af-Halogeno derivatives are frequently isolated as intermediates (81HC(37)289). 

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. 

Cyclic ethylene carbonate and its halogeno derivatives are converted into 2 2 difluoro 1,3 dioxolanes, which are useful as inhalation anaesthetics by treatment with sulfur tetrafluonde m an anhydrous hydrogen fluoride solution at 100-150 °C [239] (equation 126)... 

Simple isothiazole-4-carboxylic acids have been made from the corresponding nitriles, which are available in turn from the halogeno derivatives, or directly by the olefin route.5-Aminoiso-thiazole-4-esters and -nitriles are readily obtained by the thioamide route. The 4-acids behave normally and form acid chlorides, esters, amides, and hydrazides. In contrast to the 5-series... 

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 2-halogeno derivatives of thieno[3,2- ]pyridine are accessible through the lithium derivatives (84JHC785). 

Halogenation of diphenyl or methyl phenyl sulphoxides by Cl2 or Br2 affords mainly para-halogeno derivatives, whereas the meta-isomers are formed in low percentages or not at all606,607. In contrast, nitration in concentrated sulphuric acid leads to metasubstitution whose extent increases with acidity of the medium (up to 100%)6°8. 

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... 

A. 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... 

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... 

The halogeno derivatives 56b and 56d are excellent candidates for the synthesis of other derivatives of the nido-C4B2 cluster series bearing functional groups either in the 6- or the 1,6-positions. With few exceptions, the reactions of 56d with nu-... 

Deinsertion is not limited to hydrido complexes since alkyl and halogeno derivatives undergo the same type of reaction ... 

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. 

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