Dioxo 1-oxid

Boron trioxide is not particularly soluble in water but it slowly dissolves to form both dioxo(HB02)(meta) and trioxo(H3B03) (ortho) boric acids. It is a dimorphous oxide and exists as either a glassy or a crystalline solid. Boron trioxide is an acidic oxide and combines with metal oxides and hydroxides to form borates, some of which have characteristic colours—a fact utilised in analysis as the "borax bead test , cf alumina p. 150. Boric acid. H3BO3. properly called trioxoboric acid, may be prepared by adding excess hydrochloric or sulphuric acid to a hot saturated solution of borax, sodium heptaoxotetraborate, Na2B407, when the only moderately soluble boric acid separates as white flaky crystals on cooling. Boric acid is a very weak monobasic acid it is, in fact, a Lewis acid since its acidity is due to an initial acceptance of a lone pair of electrons from water rather than direct proton donation as in the case of Lowry-Bronsted acids, i.e. 

Oxidation of olefins and dienes provides the classic means for syntheses of 1,2- and 1,4-difunctional carbon compounds. The related cleavage of cyclohexene rings to produce 1,6-dioxo compounds has already been discussed in section 1.14. Many regio- and stereoselective oxidations have been developed within the enormously productive field of steroid syntheses. Our examples for regio- and stereoselective C C double bond oxidations as well as the examples for C C double bond cleavages (see p. 87f.) are largely selected from this area. 

Isopropylidene or benzylidene 2-hydrazinoselenazole derivatives can be converted to highly colored 2.2 -dioxo-A-3,3 -biselenazol-5,5 -inylidene-bis-hydrazones (Table X-11) by oxidation with ferric chloride and hydrogen peroxide i33). 

Of the three benzenetricarboxyhc acids, only trimellitic acid as the anhydride is commercially produced in large volume, by Hquid-phase air oxidation of either pseudocumene or dimethyl benzaldehyde. The pseudocumene oxidation is another variant of the cobalt—manganese—bromine catalyst in acetic acid solvent as described in the terephthaUc acid section. The acid is available as a laboratory chemical (99). The lUPAC name of trimellitic anhydride is 5-isobenzofurancarboxyhc acid (l,3-dihydro-l,3-dioxo). 

Tetracyanobenzoquinone [4032-03-5] 3,6-dioxo-l,4-cyclohexadiene-l,2,4,5-tetracarbonitrile, is a remarkably strong oxidizing agent for a quinone it abstracts hydrogen from tetralin or ethanol even at room temperature (50). It is a stronger TT-acid than TCNE because it forms more deeply colored TT-complexes with aromatic hydrocarbons. 

The isoxazoles (585) were formed regioselectively from the (dioxoalkyl)phosphonium salts (584) with hydroxylamine hydrochloride, the direction of cyclization being different from that of the nonphosphorus-containing 1,3-dioxo compound (see Chapter 4.16). Aqueous sodium hydroxide converted (585) into the isoxazole (586) and triphenylphosphine oxide. Treatment of (585) with n-butyllithium and an aldehyde gave the alkene (587). With hydrazine or phenylhydrazine analogous pyrazoles were formed (80CB2852). 

Oxidation of perfbtoroquinobne by fuming nitric acid yields pentafluoro-5,8-dioxo-5,8-dihydroquinoline or hexafluoro-2 oxo-l,2-dihydroquinoline in low yields ]98 (equation 90)... 

In this connection the possibility of oxidation of these substances to the tetrahydro derivatives should be mentioned. It was made use of by Thiele and Bailey for the preparation of 6-methyl-3,5-dioxo-2,3,4,5-tetrahydro-l,2,4-triazine (6-azathymine) (46) and only recently by Grundman et al. for that of 6-azauracil (42). 

In this connection it is important to mention the finding that the thioxo derivatives (52) can be converted in several ways to the 3,5-dioxo derivatives. By alkylation with methyl iodide in alkaline solution, methylmercapto derivatives (53) are produced which are readily hydrolyzed to dioxo derivatives. A similar course is followed in the reaction with ethyl chloroacetate. Finally, oxidation with hypo-... 

Oxidation of the hexahydro to tetrahydro derivatives was mentioned in connection with the synthesis of 3,5-dioxo-l,2,4-triazines (e.g., Section II,B,2,a). The reverse procedure, hydrogenation of the tetrahydro derivatives, was used with 6-azauracil, 6-azathymine, and their iV-methyl derivatives. With all these compounds hydrogenation proceeds smoothly in the presence of Adams catalyst. Only the hydrogenation of l-methyl-6-azathymine was not successful. ... 

When, aiming at its cardiotonic activity (stimulant), the 2,5-dioxo-l,2,5,6,7,8-hexahydro-3-cyano-6-bromoquinoline is made to react with different thioamides, the appropriate 6-substituted 8,9-dihydro- (R = cyanomethyl-, 2-oxopyrrolidinyl-methyl-, 2-oxohexahydroazepinomethyl-, and thioxopyrrolidinylmethyl-) (94KFZ43) or (R = H, Me, NH2, NH/S ) (86JAP(K)1, 89H1517) thiazolo[4,5-/Iquinolines 37 or oxidized products (89H1517) are produced. 

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. ... 

There is a vigorously expanding chemistry of compounds of ruthenium and osmium in high oxidation states [3, 4, 11, 12], particularly of dioxo and nitrido compounds, though recently some striking developments have taken place in imide chemistry. 

Athyl-5-phenyl-barbitursaure liefert durch Reduktion mit einem kleinen OberschuB an Natriumboranat/Bortrifluorid 2,4-Dioxo-5-dthyl-5-phenyl-hexahydro-pyrimidin. Zum Gelingen der Reaktion muB der reduzierte Ansatz mit alkalischem Wasserstoffper-oxid oxidiert werden (s.S. 58, 81). Die Reduktion gelingtmeist nur bei 5-Phenyl-barbitur-sauren3. 

Oxidation of oxyberberine (58) with lead tetraacetate effected 13-acetoxyl-ation to give 13-acetoxyoxyberberine (116), which was further oxidized to the 14-alkoxy-8,13-dioxo compounds 117 and 118 (Scheme 25). Reduction of 116 with lithium aluminum hydride followed by sodium borohydride afforded ( )-ophiocarpine (92) (78). 

Scheme 8 displays reactions where 43 behaves as a source of a Zr(II) derivative.30 They can be formally viewed as oxidative additions to the [p-Bu -calix[4]-(0Me)2(0)2Zr] fragment. The main driving force in the case of ketones is the high oxophilicity of the metal, which induces the reductive coupling of benzophenone leading to 45, or the addition of dibenzoyl causing the formation of the dioxo-metallacycle in 46, which contain a C-C double bond. It has to be mentioned that... 

The fungal metabolite, 5-A-acetylardeemin, possessing a hexacyclic structure with a l,4-dihydro-3,6-dioxo-pyra-zino[2,l-A]quinazoline skeleton, is the best multidrug resistance reversal agent known to date <1998MI45>. Hexahydro-3,6-dioxo-pyrazino[2,l-7]quinazolines have been claimed as endothelial nitric oxide synthetase regulators useful in the treatment of cardiovascular disorders <2004EP1471066>. 

Dioxo-ruthenium porphyrin (19) undergoes epoxidation.69 Alternatively, the complex (19) serves as the catalyst for epoxidation in the presence of pyridine A-oxide derivatives.61 It has been proposed that, under these conditions, a nms-A-oxide-coordinated (TMP)Ru(O) intermediate (20) is generated, and it rapidly epoxidizes olefins prior to its conversion to (19) (Scheme 8).61 In accordance with this proposal, the enantioselectivity of chiral dioxo ruthenium-catalyzed epoxidation is dependent on the oxidant used.55,61 In the iron porphyrin-catalyzed oxidation, an iron porphyrin-iodosylbenzene adduct has also been suggested as the active species.70... 

Oxidizing enzymes use molecular oxygen as the oxidant, but epoxidation with synthetic metalloporphyrins needs a chemical oxidant, except for one example Groves and Quinn have reported that dioxo-ruthenium porphyrin (19) catalyzes epoxidation using molecular oxygen.69 An asymmetric version of this aerobic epoxidation has been achieved by using complex (7) as the catalyst, albeit with moderate enantioselectivity (Scheme 9).53... 

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