2,4-Dibromo-2,4-dimethyl-3-pentanone

The first synthesis of 4-isoxazolidinones (540) resulted from the reaction of 2,4-dibromo-2,4-dimethyl-3-pentanone with hydroxylamine (81H(16)1855>. 

Reduction of 2-bromo-3-pentanone at mercury affords a mixture of 3-pentanone and l-hydroxy-3-pentanone, whereas electrolysis of Q ,Q -dibromoacetone in the presence of benzoate gives a mixture of products arising from both a carbon-bromine bond cleavage and an Sn2 displacement of bromide by benzoate [94]. In an acetic acid-acetate buffer, branched dibromo ketones, such as 2,4-dibromo-2,4-dimethyl-3-pentanone, are reduced to a-acetoxy ketones however, less highly substituted compounds, such as 4,6-dibromo-5-nonanone, undergo simple cleavage of both carbon-bromine bonds [95]. Other work dealing with the reduction of Q, Q -dibromoketones has been described [96]. 

Dihaloketones. A number of studies of the electroreduction of a,a -dibromoketones have been reportedly directed to obtaining evidence for the the intermediacy of cyclo-propanone-derived intermediates (186). Reduction of 2,4-dibromo-2,4-dimethyl-3-pentanone (185) consumed two Faradays of current and gave a species which is briefly stable at -32 °C. The intermediate (186) could be intercepted by subsequent addition of a protonic trapping agent to the low-temperature catholyte (equation 100). Results have... 

A soln. of 2,4-dibromo-2-methyl-3-pentanone in dimethylformamide added drop-wise under Ng at -35° to a suspension of zinc-copper couple in dimethylformamide, and stirring continued 10 min. at the same temp. 4-ethylidene-5,5-dimethyl-2-dimethylamino-l,3-dioxolane. Y ca. 50%. F. e. s. H.M.R. Hoffmann et al., Am. Soc. 94, 3201 (1972). 

A soln. of 2,4-dibromo-2,4-dimethyl-3-pentanone in N-methylformamide, a polar, weakly protic solvent, stirred below -5° under N2 into a suspension of zinc-copper couple in the same solvent, and the product isolated after 2 hrs. 2,4,4,5,5,7-hexamethyl-3,6-octanedione. Y 71%. F. e. s. C. Chassin, E. A. Sdimidt, and H. M. R. Hoffmann, Am. Soc. 96, 606 (1974). 

Dibromo-2,4-dimethyl-3-pentanone electrolyzed in a 1 M soln. of Na-acetate in acetic acid at -1.8 v. with a Pt-gauze anode and a Hg-pool cathode in a divided cell until the current reaches a constant value of ca. 2 mA 2-acetoxy-... 

Under acidic conditions, one bromine atom replaces a hydrogen atom at C-4 to give 2-bromo-4,4-dimethyl-3-pentanone. Under basic conditions, the reaction continues to replace the second hydrogen atom faster than the first, and a dibromo compound is obtained. 

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