Halo oximes

Another transformation of BENA is observed in the reactions of Nu having a lower nucleophilicity toward silicon (path (b)). This reaction produces the cation B as the key intermediate, which is more reactive than nitrosoalkene (511). As a result, two by-products, viz., a-siloxy oxime (504) and a-halo oxime (514), are generated along with the target salt (512). ... 

Earlier, another scheme was suggested for the generation of salts (513) based on oximino-alkylation of Nu with halo-oximes (504) (453). However, special experiments demonstrated that this reaction requires more severe conditions (536) and does not proceed during the real generation of salts (513). 

Nitrosoalkenes 192, generated in situ from a-halo oximes, reacted with methox-yallene in a [4+ 2] fashion to give 6H-l,2-oxazines [156]. 

Nitrosoalkenes.1 Nitrosoalkenes are usually generated by reaction of a-halo oximes with bases, and have been used for [4 + 2] cycloadditions. They are also generated efficiently from a-chloro silyloximes by fluoride ion. This elimination is used to effect an intramolecular cyclization of the nitrosoalkene generated from 1 to give a mixture of the dihydrooxazines 2 and 3. The choice of the metal fluoride is critical for acceptable yields. Highest yields are obtained when the nitrosoalkene is generated slowly by a... 

Domino [3+2] cycloaddition/annulation reactions of aminophenyl-ynones 23 with nitrile oxides, generated in situ from chloro oximes 22, allowed the synthesis of isoxazolo[4,5-c]quinolines 24, in satisfactory yields <03EJO1423>. Bromine substituents on naphthoquinones activate and orient 1,3-DC with nitrile oxides. Compound 25 reacted with halo oximes 22 to give regioselectively only unsymmetrical naphthoquinones 26, as polyketide building blocks <03TL8901>. 

Synthetic methods which utilize the addition of nucleophiles to a-halo oximes and similar compounds (the Hoch-Campbell reaction) have been reviewed. ... 

Nitrile oxides (R-C=N -0"), ° which can be generated by base-catalysed elimination of hydrogen halide from halo-oximes (RC(Hal)=NOH), or by dehydration of nitro componnds (RCH2NO2), readily add to alkenes and to alkynes, generating tive-membered heterocycles. Addition to an alkene produces an isoxazoline, unless the alkene also incorporates a group capable of being eliminated in a step after the cycloaddition, as shown below. However, isoxazolines can also be dehydrogenated to the aromatic system. ... 

BSB5l>. As in the earlier examples, the nitrosoalkene was generated in situ by base-induced elimination of HCl from the corresponding a-halo oxime. 

This reaction bears an analogy to the reaction of a-halo oximes with a nucleophile, for example, the conversion of (A) to (B). ... 

The Jorgensen group revealed the first example of an asymmetric inverse-electron-demand HDA reaction for the synthesis of 5,6-dihydro-4H-oxazines in the presence of la (Scheme 9.47). The reaction between isovaleraldehyde and the aromatic ot-halo-oxime proceeded smoothly to produee, after oxidation with PCC, oxazinone with moderate enantioselectivity (42% ee). 

Et) to 3/-chiral acyclic nitrosoalkenes, such as PhCH(Me)CH=CHNO, generated in situ from the corresponding a-chloro oxime derivatives, for example, PhCH(Me)CH(Cl)CH=N-0-t-butyldimethylsilyl (NOTES), and potassium bis(trimethylsilyl)amide (KHDMS) and BU4NF, have been found to afford exclusively the anti-products.In a similar way, addition of 5-nucleophiles 0 R SH to nitroalkenes R CH=CR NO, generated in situ from cr-halo oximes R CH(X)C(R )=NOH on treatment with NaHC03, can be catalysed by chiral thioureas. The resulting a-sulfenylated oximes R CH(SR )C(R )=NOH were obtained with <82% eeP (J)... 

The extraction of metal ions depends on the chelating ability of 8-hydroxyquinoline. Modification of the stmcture can improve its properties, eg, higher solubility in organic solvents (91). The extraction of nickel, cobalt, copper, and zinc from acid sulfates has been accompHshed using 8-hydroxyquinohne in an immiscible solvent (92). In the presence of oximes, halo-substituted 8-hydroxyquinolines have been used to recover copper and zinc from aqueous solutions (93). Dilute solutions of heavy metals such as mercury, ca dmium, copper, lead, and zinc can be purified using quinoline-8-carboxyhc acid adsorbed on various substrates (94). 

Although 3y5-hydroxy-A -l9-aldehydes can be obtained from the corresponding oxime by acid treatment, the most efficient method for the production of A -19-aldehydes is nitrosation of the oximes followed by zinc reduction of the 5a-halo hemiacetal. ... 

Indirect conversion of oximes to nitro compounds viact-halo nitro compounds has provided a useful method for synthesis of nitro compounds, as shown m Scheme 2 1... 

There are three possible products when NOCl is added to alkenes. The initial product is always the [3-halo nitroso compound, but these are stable only if the carbon bearing the nitrogen has no hydrogen. If it has, the nitroso compound tautomerizes to the oxime ... 

Iodofurazans react with nucleophilic reagents differently from other halo- and nitrofurazans. For instance, treatment of 3-amino-4-iodofurazan 25 with sodium ethoxide at room temperature did not yield the expected ethoxy derivative 26 but led to the ring-open product, that is, the sodium salt of a-amino-a-hydroxyimino- acetonitrile 27 (Scheme 9). Acidification of salt 27 gave cyano oxime 28 <2004RCB1124>. 

A convenient procedure for catalytic carbonylation of bromooxazines (520) giving rise to previously unknown methoxycarbonylmethyl-substituted oxazines (525) in good yields (538) deserves note, all the more because this is the first example of catalytic C,C-coupling reactions of ethers of a-halo substituted oximes. 

The reaction of a-halo ketone oximes 204 with isocyanides leads to formation of 5-aminoisoxazole derivatives 205. The reaction involves formation of nitrosoalkenes as intermediates (equation 89) ". ... 

Reaction of amidoximes with dicarbonyl compounds in the presence of Ru3(CO)i2 afforded pyrimidine derivatives" . Reaction of oximes of type RCH=CMeC(=NOH)Me with R NCN also leads to pyrimidines" . a-Halo- and dihaloketoximes and Grignard reagents undergo dimerization to 2,4,6-trisubstituted pyrimidines" " For example. 

Usually, 3- and 4-substituted thianes are prepared from the 3- and 4-oxothians by the common techniques applicable to alicyclic chemistry. Reduction affords alcohols which may be etherified or halogenated, while oximation and reduction produces the amino derivatives, which are also accessible via the halo compounds. 2-Alkoxy and 2-alkylthio compounds are made by acid catalyzed addition of alcohols and thiols to 3,4-dihydro-2H-thiopyran (75MI22502) in a reaction analogous to the use of dihydropyran for protection of alcohols as THP ethers. 

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