1.1- dibromo-3,5-dioxo

Early investigators adduced various kinds of chemical evidence in support of a monohydroxy-dioxo structure for barbituric acid (112) (a) reaction with diazomethane afforded a mono-O-methyl deriva- iye,i59,i6o barbituric acid and its 5-alkyl derivatives are much stronger acids than the 5,5-dialkyl derivatives, and (c) the 5-bromo and 5,5-dibromo derivatives have different chemical properties. - The early physical evidence also appeared to substantiate the monoenol structure, this formulation having been suggested for barbituric acid in 1926 on the basis of its ultraviolet spectrum and again in 1934, In the 1940 s, ultraviolet spectroscopic studies led to the suggestion of other monohydroxy and dihydroxy structures for barbituric acid, whereas its monoanion was assigned structure 113 (a clear distinction between ionization and tautomerism was not made in these papers). 

The enone 445 was then converted to ( )-oxocrinine (415) by a sequence that commenced with the bromination of 445 using excess 5,5-dibromo-2,2-di-methyl-4,6-dioxo-l,3-dioxane to provide a mixture of bromo ketones 446. Removal of the jV-carbobenzyloxy protecting group according to the protocol previously detailed gave 448 as a mixture (a-Br (3-Br = 3 1) of diastereomers, but only the a-bromo isomer underwent dehydrobromination on heating with lithium bromide and lithium carbonate in dry DMF to furnish 415. Interestingly, treatment of the (3-bromo derivative of 448 under similar conditions afforded the debrominated product 447 (200). 

Telturinane l,l-Dibromo-3,5-dioxo-2-methyi- E12b, 556 (Bromie-rung)... 

Benzocyclobutene 3,6-Dibromo-4,5-dichloro-l,2-dioxo- E17f., 973 (Cl4 -> Dioxo)... 

Dibromo-4,5-dioxo-2,6-cyclo-hepladien-ylidene)-l,2-diphenyl-2976, 3158 C22H,2F,... 

Dimedone was treated with two equivalents of bromine in glacial acetic acid to yield 2,2-dibromo-5,5-dimethylcyclohexane-l,3-dione. The dibromo compound was subjected to reaction with substituted 2-aminothiophenols, 2-aminophenol, thiocarbohydrazones, and triazoles to furnish spiro-(2, 6 -dioxo-4, 4 -dimethylcyclohexane)-6-substituted-l,... 

Photo-catalytic bromination of epoxides derived from terminal alkenes results in the formation of ketones brominated exclusively on the less substituted a-carbon atom [equation (47)]. 5,5-Dibromo-2,2-dimethyl-4,6-dioxo-l,3-dioxan (32) has been shown to monobrominate saturated aldehydes and ketones... 

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