L-Bromo-2-butanone

A useful pyrimidine precursor is 2,4-diamino-6-oxo-pyrimidine. Heating a mixture of this pyrimidine and l-bromo-2-butanone in DMF afforded 2-amino-6-ethyl-3,4-dihydro-4-oxo-7(7/)-pyrrolo[2,3-,y pyrimidine in modest yield <2006JMC1055>. 

Butane-2-one, for example, thus gives a mixture containing 3-bromo-2-butanone as main product (see substitution rules on page 190) with some l-bromo-2-butanone, and the mixture can be separated by distillation at 150 mm through an efficient column with a reflux ratio of 6 l.681 Monobromoacetone can also be prepared in this way. 

Easily available copper(II) tartrate has also been used for an enantioselective cyclopropanation. From 3-methoxystyrene and 4-bromo-l-diazo-2-butanone, the cyclopropanes cis/trans-204 were obtained the mainly formed frans-isomer displayed an enantiomeric excess of 46% i99>. This reaction constituted the opening step of asymmetric total syntheses of equilenin and estrone. 

Intermolecular cyclopropanation of diazoketones is an effective method in organic synthesis. Wenkert and coworkers have applied this methodology to the synthesis of a substantial number of cyclopropane adducts 2868, 2969 and 307° which are synthetic intermediates in the preparation of natural products (equations 41—43). Copper catalysts were chosen for these transformations. Another interesting application of intermolecular cyclopropanation is to be found in Daniewski s total synthesis of an aromatic steroid. Palladium(II) acetate catalysed decomposition of 4-bromo-l-diazo-2-butanone in the presence of m-methoxystyrene was used to give the cyclopropyl ketone 31 which was a key intermediate in the total synthesis (equation 44)71. 

Examples of the solvent-dependent competition between nucleophilic substitution and / -elimination reactions [i.e. SnI versus Ei and Sn2 versus E2) have already been given in Section 5.3.1 [cf. Table 5-7). A nice example of a dichotomic y9-elimination reaction, which can proceed via an Ei or E2 mechanism depending on the solvent used, is shown in Eq. (5-140a) cf. also Eqs. (5-20) and (5-21) in Section 5.3.1. The thermolysis of the potassium salt of racemic 2,3-dibromo-l-phenylpropanoic acid (A), prepared by bromine addition to ( )-cinnamic acid, yields, in polar solvents [e.g. water), apart from carbon dioxide and potassium bromide, the ( )-isomer of l-bromo-2-phenylethene, while in solvents with low or intermediate polarity e.g. butanone) it yields the (Z)-isomer [851]. 

Carbocycles (see also Diels-Alder reaction) Allme. Bistripbenylphosphinedicarboiiyl-nickel. 4-Bromo-2-butanone ethylene ketal. Dkbloroketene. Diiron nonacarbonyl. 3,5-Di-inethyl-4-chloroinethylisoxazole. Nickel carbonyL Vinyl l carbomethoxyethyl ketone. Carboethoxyazepine Ethyl azidoformate. 

Bromoadenosine monophosphate, 99 3-Bromo-2-butanone-l,4-diol diethyl ketal, synthesis of, 393, 394 Bromocolchicine, 567-571 binding to brain extracts, 570,571 synthesis of, 569 Bromoconduritol, 369,370 inhibition of glucosidase, 381 synthesis of, 380, 381 a-Bromo-ft>-(3-cyanophenyl)alkane, 122 6-Bromo-6-deo conduritol B epoxide, active site labeling, 377-380 3-Bromo-l,4-dihydroxy-2-butanone 1,4-bisphosphate, 142, 392, 396, 397 synthesis of, 392-395... 

Dimethylaminoethylthiazoles (17) were prepared from thioamides and l-bromo-4-dimethylamino-2-butanone (16), with R, =Me, CH2Ph, (CH2)NHCOPh, and (Ac)2NCH2 (Scheme 9) (337, 392). 

To the solution is added 900 ml. of water, and the resulting mixture is washed with four 500-ml. portions of ether. The ether layers are combined and washed with 200 ml. of aqueous 10% potassium carbonate and then twice with 200-ml. portions of water (Note 9). The ether layer is dried for 1 hour over 200 g. of anhydrous calcium chloride (Note 10) and the solvent is removed on a rotary evaporator at room temperature to give 145-158 g. of crude product (Note 11). Distillation under reduced pressure through a Vigreux column gives 115-128 g. of a fraction, b.p. 83-86° (54 mm.), w22 d 1.4620-1.4640, containing 95% of l-bromo-3-methyl-2-butanone as established by proton magnetic resonance measurements (Note 11). 

Butanone, 3-bromo-, 55, 129 2-BETANONE, l-bromo-3-methyl-, 55, 24 2-Butanone, 3-bromo-3-methyl-, 55, 25... 

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