2.4- Dimethylpentan-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... 

Ketonic hydrolysis to di-isopropyl ketone. Mix 14 g (0.75 mol) of the ester with 30 ml of glacial acetic acid, 10 ml of water and 10 ml of concentrated sulphuric acid, and boil under reflux until evolution of carbon dioxide ceases. Dilute the cooled solution with 180 ml of water, add 100 ml of ether and render alkaline to phenolphthalein with 20 per cent sodium hydroxide solution. Separate the ether layer, extract the aqueous layer with two 50 ml portions of ether, dry the combined ether layer and extracts with anhydrous sodium sulphate, distil off the ether and fractionate the residue. The yield of di-isopropyl ketone (2,4-dimethylpentan-3-one), b.p. 123-124 °C, is 6.5 g (76%). 

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. 

Radical Additions. Batchelor and Fischer [109] measured absolute rate constants kaM for addition of 2-hydroxy-2-propyl radicals 21 to alkenes by a new method, using time-resolved CIDNP. Photoexcited 2,4-dihydroxy-2,4-dimethylpentan-3-one 20 served as a source of these radicals. Chart XI summarizes the relevant steps of the underlying reaction scheme in a simplified manner. Their key idea was to evaluate not the net polarizations, which may be strongly distorted by nuclear spin relaxation in the radicals, but the multiplet polarizations, which had previously [110] been shown to be uninfluenced by relaxation at the paramagnetic stage provided that the... 

Dimethyl pentanedioate. See Dimethyl glutarate 2,4-Dimethylpentan-3-one 2,4-Dimethyl-3-pentanone. See Diisopropyl ketone Di (4-methyl-2-pentyl) maleate. See Dimethyl amyl maleate... 

Dimethylpentan-3-one Heptan-2-one Heptan-3-one Heptan-4-one 5-Methylhexan-2-one Butyl propanoate... 

Isobutyric acid see 2-Methylpropanoic acid Isobutyron see 2,4-Dimethylpentan-3-one Isohexane see 2-Methylpentane Isohexyl alcohol see 2-Ethylbutan-l-ol Isooctane see 2,2,4-Trimethylpentane Isopentane see 2-Methylbutane Isopentanol see 3-Methylbutan-l-ol Isopentyl alcohol see 3-Methylbutan-l-ol Isoprene see 2-Methylbuta-1,3-diene Isopropanol see Propan-2-ol Isopropenylbenzene... 

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