A-Hydroxyimino carbonyl compounds

Sugamoto and colleagnes have attempted the rednction-nitrosation of the conjn-gated olefins 33 by the nse of f-bntyl nitrite instead of oxygen (Scheme 24). Various olefins such as styrenes, a,-unsaturated carbonyl compounds and a, S,y,5-unsaturated carbonyl compounds were directly converted to the corresponding acetophenone oximes, a-hydroxyimino carbonyl compounds and y-hydroxyimino-a,/S-unsaturated carbonyl compounds in good or moderate yields by rednction-nitrosation with f-butyl nitrite and triethylsilane in the presence of cobalt(II) porphyrin as a catalyst (Scheme 24). 

AMINOPYRAZINE 1 -OXIDES FROM a-AMINO NITRILES AND a-HYDROXYIMINO CARBONYL COMPOUNDS... 

Detailed discussion of the preparation of a variety of alkyl- and arylpyrazines by primary syntheses, principally from aliphatic components, appears in Chapter II. These include, for example, the preparation of 2,5-disubstituted and 2,3,5,6-tetrasubstituted alkyl- and arylpyrazines from a-amino carbonyl compounds, which may be produced by many methods such as reduction of a-hydroxyimino carbonyl compounds, aminolysis of a-halogeno carbonyl compounds, oxidation of a-amino... 

Preparations of pyrazine A -oxides containing extranuclear hydroxyl groups are also described in Qiapter III as follows Section III.l, 2-aminopyrazine 1-oxides from a-amino nitriles and a-hydroxyimino carbonyl compounds (540, 541) Section III.2, 3-substituted pyrazine 1-oxides from 2-amino-2-deoxy-D-glucose(or mannose) oxime with glyoxal (543, 544) and Section III.5, ring closure of the C-C-N-C-C-N-0 system (553). 

Preparations of C-acylpyrazines by primary syntheses have been described in Section II.IB by reduction of a-hydroxyimino carbonyl compounds (226-230). In addition to these preparations, reduction of 3-nitrosopentane-2,4-dione (prepared by nitrosation of pentane-2,4-dione) over Pd/C in an autoclave gave 2,5-diacetyl-3,6-dimethylpyrazine, and 2-nitroso-l-phenylbutane-l,3-dione (from 1 -phenylbutane-1,3-dione) similarly treated gave 2,5-dibenzoyl-3,6-dimethylpyrazine (1064). 

Primary syntheses of alkoxycarbonyl-2-aminopyrazine 1-oxides from a-amino nitriles and a-hydroxyimino carbonyl compounds have been described in Section III.1 (Table III.l) (531, 537-541). 

Cyanopyrazine A -oxides have been prepared from a-amino nitriles and a-hydroxyimino carbonyl compounds as summarized in Section III. 1 (528-530, 532-534, 537, 540, 542). Oxidation of 2-cyanopyrazine with perhydrol gave 3-cyanopyrazine 1-oxide (575), 2-cyano-5-ethoxy-3,6-dimethylpyrazine with 30% hydrogen peroxide in acetic acid at 55° gave 2-cyano-5-ethoxy-3,6-dimethylpyrazine iV-oxide (288), and the oxidations of 2-amino-3-cyanopyrazine 1-oxide (538) and... 

The required a-amino aldehydes or ketones are usually prepared in situ because of their instability they are obtained from a-hydroxycarbonyl compounds and ammonium acetate or by catalytic reduction of a-hydroxyimino- or a-azido-carbonyl compounds. 

I.3.4.2.5. Carbonyl and Thiocarbonyl Compounds a-(Hydroxyimino)phenyl-acetonitrile oxide (generated in situ at room temperature from PhC( NOH)C ( NOH)Cl in the presence of NaHC03 or Et3N) reacts with simple aldehydes and ketones R1R2CO to give 1,4,2-dioxazoles 180 (347). Related dioxazoles, formed by cycloaddition of benzonitrile oxide to aromatic aldehydes, upon treatment with I-BuOK, undergo cyclo-reversion, allowing direct conversion to substituted benzoic acids or their esters (348). 

The hydroxyimino group attached to carbon (C=NOH) may be converted into an amino group by way of the intermediate hydroxyamino or imino group. The reduction of oximes can be conducted so as to yield (1) a synthesis of amines from carbonyl compounds, (2) introduction of amino groups into a compound containing active methylene groups (by way of the isonitroso compounds obtained by nitrosation), or (3) production of amines from the adducts of nitrogen oxides or nitrosyl chloride to olefins. 

For oximes, the word oxime is placed after the name of the aldehyde or ketone. If the carbonyl group is not the principal group, use the prefix hydroxyimino-. Compounds with the group Z = N—OR are named by a prefix alkyloxyimino- as oxime O-ethers or as O-substituted oximes. Compounds with the group r C=N(0)R are named by adding A-oxide after the name of the alkylideneaminc compound. For amine oxides, add the word oxide after the name of the base, with locants. For example, C5H5N—O is named pyridine A-oxide or pyridine 1-oxide. 

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