A Dioxo compounds

In a preliminary communication, the dihydroxy-1,2,4-triazine derivative 163 has been assigned the structure shown on the basis of infrared evidence. The pK and ultraviolet and infrared spectral data support the formulation of 6-azauracil (164) as a dioxo compound. 

Pyrazino[2,3-rf]pyridazine derivatives are also obtained by cyclocondensation of 4,5-diamino-pyridazines with a-dioxo compounds. Thus, 4,5-diamino-3-chloro-1 -methyl-6( 17/)-pyridazinone (96) and benzil (95) at reflux temperature in acetic acid give a 97% yield of pyrazino[2,3-d]py-ridazinone (97) (Equation (12)) <90MI 719-03). 

Enolizable a-dioxo compounds, such as biacetyl and 1-phenylpropane-l, 2-dione, condense with iV2-phenylpyridine-2,3-diamine (20) in refluxing ethanol to give 2-methyl-3-methylene-4-phenyl-3,4-dihydropyrido[2,3-6]pyrazine (21a) and 3-methylene-2,4-diphenyl-3,4-dihydropyrido[2,3-A] pyrazine (21b), respectively, in low yield.21... 

N-Aminophenylaziridine a-Diazoketones from a-dioxo compounds Ethylene derivatives from N-aminoaziridines... 

Diazoketones from a-dioxo compound monohydrazones s. 16, 360 Manganese dioxide Mn02... 

Potassium tert-butoxide Pyrroles from a-dioxo compounds... 

Torgov introduced an important variation of the Michael addition allylic alcohols are used as vinylogous a -synthons and 1,3-dioxo compounds as d -reagents (S.N. Ananchenko, 1962, 1963 H. Smith, 1964 C. Rufer) 1967). Mild reaction conditions have been successful in the addition of ],3-dioxo compounds to vinyl ketones. Potassium fluoride can act as weakly basic, non-nudeophilic catalyst in such Michael additions under essentially non-acidic and non-basic conditions (Y. Kitabara, 1964). 

The addition of large enolate synthons to cyclohexenone derivatives via Michael addition leads to equatorial substitution. If the cyclohexenone conformation is fixed, e.g. as in decalones or steroids, the addition is highly stereoselective. This is also the case with the S-addition to conjugated dienones (Y. Abe, 1956). Large substituents at C-4 of cyclic a -synthons direct incoming carbanions to the /rans-position at C-3 (A.R. Battersby, 1960). The thermodynamically most stable products are formed in these cases, because the addition of 1,3-dioxo compounds to activated double bonds is essentially reversible. 

The usefulness of the Knorr synthesis arises from the fact that 1,3-dioxo compounds and a-aminoketones are much more easily accessible in large quantities than rational 1,4-difunctional precursors. Such practical syntheses are known for several important hetero-cycles. They are usually limited to certain substitution patterns of the target molecules. 

Substituted quinoxalines afford mono-A -oxides, presumably the 1-oxides, and are resistant to further oxidation, though 5-methoxyquinoxaline is exceptional in forming a 1,4-dioxide. In the case of 6-substituted quinoxalines, as the substituent becomes more electron attracting, the yields of 1,4-dioxide decrease but more of the corresponding 2,3-dioxo compound (41) is formed. ... 

Dioxo-3-isoparteine was isolated from Lupinus sericeus (143). The mass spectrum, with M+ at miz 262 and signals at miz 234 (M" — 28) and 206 (M+ - 56), is characteristic for 10- and 17-oxosparteines and successive splitting of two carbonyl groups. Oxidation of p-isosparteine (14) by potassium ferricyanide resulted in 10-oxosparteine (108) as well as 10,17-dioxo-p-isospar-teine (109) (Scheme 13). This confirmed the alkaloid structure. Although 109 was found as a natural compound it had already been synthesized by Bohlmann et al. (144). The problems of configuration and conformation of sparteine (6), a-isosparteine (7), and (3-isosparteine (14) were discussed (145). 

Methylene groups adjacent to the N atom in tertiary polycyclic amines were oxidised by RuO /aq. Na(IO )/CCl, depending on reaction conditions. Thus A -benzyl-9-azabicyclo-[l, 3, 3]-nonane yielded AT-benzoyl-9-azabicyclo-[l, 3, 3]-nonane (Fig. 5.5) and A -benzyl-l,3-dioxo-iso-quinoline gave the A -benzoyl compound, while A -benzyl-5,6-dihydro-llH-dibenz[b,e]azepine, which has exi and endocydic benzyl groups, were oxidised to the N-benzyl-6-oxo derivative [41]. 

Dioxo compound 130 was converted to 7 in 80% yield by treatment with /n-chloroperbenzoic acid (wi-CPBA). According to the literature, six-membered rings containing a 1,2-dicarbonyl moiety are converted to five-membered ring hydroxy acids only in the presence of a strong base [71]. By contrast, our method is performed under neutral conditions and is more efficient. 

In contrast to the situation a decade ago, many incomplete cubane-type clusters with Mo304 S cores have been prepared and the structures have been determined by X-ray structure analyses. The results obtained are summarized in Tables I—III. The formal oxidation state of molybdenum in the compounds cited here is in all cases IV. Unlike Mo(VI) and Mo(V) compounds, mononuclear oxo or dioxo compounds of the Mo(IV) state are relatively rare and all the incomplete cubane-type compounds cited here have no terminal oxo ligand. Three Mo atoms form an equilateral triangle, and three single bonds exist between each Mo. Except for the compounds 1, 8, and 31 (Table III), and excluding Mo—Mo bonds, each molybdenum is octahedrally coordinated. 

The problems involved are exemplified here by Knorr s pyrrole synthesis (A. Gossauer, 1974). It has been known for almost a century that a-aminoketones (C2N components) react with 1,3-dioxo compounds (C2 components) to form pyrroles (C4N-heterocycles). A side-reaction is the cyclodimerization of the a-aminoketones to yield dihydropyrazines (C4Nj), but this can be minimized by keeping the concentration of the ar-aminoketone low relative to the 1,3-dioxo compound. The first step in Knorr s pyrrole synthesis is the formation of an imine. This depends critically on the pH of the solution. The nucleophilicity of the amine is lost on protonation, whereas the carbonyl groups are activated by protons. An optimum is found around pH 5, where yields of about 60% can be reached. At pH 4 or 6 the yield of the pyrrole may approach zero. The ester groups of /7-keto esters do not react with the amine under these conditions. If a more reactive 1,3-diketone is used, it has to be symmetrical, otherwise mixtures of two different imines are obtained. The imine formed rearranges to an enamine, which cyclizes and dehydrates to yield a 3-acylpyrrole as the normal Knorr product (A. Gossauer, 1974 G.W. Kenner, 1973 B). 

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