2.4- Dibromo-2,4-dimethylpentane-3-one

Tricarbonyl[t/M-(ethoxycarbonyl)-l//-azepine]iron(0) (30) with the 2-oxyallyl cation derived from 2,4-dibromo-2,4-dimethylpentan-3-one and nonacarbonyldiiron(O) yields a mixture of adducts which, after oxidative decomplexation with tetrachloro-l,2-benzoquinone (o-chloranil), affords the tetrahydrofuro[2,3-A)azcpine derivative 33 and the 3-substituted 1H-azepine-l-carboxylate 34.227... 

Cycloheptenones. Dehalogenation of z,x -dibromoketoncs with diiron nonacarbonyl in the presence of a 1,3-diene provides a direct route to seven-membered cyclic ketones. Thus the reaction of 2,4-dibromo-2,4-dimethylpentane-3-one (I), diiron... 

A similar electrochemical reduction was performed with 1,3-dibromo ketones in methanol or dimethylamine (in acetonitrile) to give cyclopropanone hemiacetals and 1-aminocyclopropan-l-ol derivatives 31. A considerable improvement in the yield was achieved when, instead of using methanol as the solvent, only a twofold excess of methanol in acetonitrile was used. The reported quantitative conversion of 2,4-dibromo-2,4-dimethylpentan-3-one to 1,2,2,3,3-pentamethylcyclopropan-l-oF in methanol could not be reproduced instead only ca. 45% yield was obtained. 

For some of the simple 4,5-dihydro-3//-pyrazoles not available by the diazoalkane-alkene route, an alternative to the hydrazine reaction discussed in the last section is oxidative cyclization of a 1,3-diamine. Hence, an alternative preparation of the ketone 1 is to react 2,4-dibromo-2,4-dimethylpentan-3-one with sodium azide, reduce the azide groups with ammonium polysul-fide " and oxidatively cyclize with sodium hypobromite. " ... 

A similar tetramethyl derivative was obtained as adduct by electrolysis of 2,4-dibromo-2,4-dimethylpentan-3-one (18) in methanol in the presence of aniline. The formation of adduct 20 might be explained by addition of methanol to the electrosynthesized tetramethylcyclo-propylideneamine 19. 

Pentamethylcyclopropanol (43) was produced in 44% yield from the reaction of 2,4-dibromo-2,4-dimethylpentan-3-one (42) with two molar equivalents of lithium dimethylcuprate in diethyl ether/furan at — 78 °C. The intermediate tetramethylcyclopropanone, formed by a two-electron reduction of the starting material, was trapped by the cuprate and also by furan to give the [3-1-4] cycloadduct 45 in 6% yield. 

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