2- Butanone, 1,3-dibromo

BUTANONE, 1 bromo 3 methyl, 55, 24 2 Butanone, 3-bromo-3-methyl-, 55, 25 2-Butanone, 1,3-dibromo-3-methyl-, 58, 22,... 

Diels and Stephan173 treated the benzoate of 3-hydroxy-2-butanone with bromine, and obtained crystalline 1-bromo- and 1,1-dibromo- derivatives. With dilute alkali, these formed 4-deoxy-DL-gZycero-tetrulose and 4-deoxy-DL-erythrosone respectively. Both compounds gave with phenylhydrazine 4-deoxy-DL-erythrose phenylosazone, which had previously been prepared from the corresponding aldotetrose.174... 

The Sn2 reaction of octa-0-(methylsulfonyl)sucrose with sodium bromide revealed further the comparative reactivities of the sulfonyloxy substituent at C-6, C-6, and other carbon atoms.97 On treatment with sodium bromide in butanone, octa-0-(methylsul-fonyl)sucrose gave 6,6 -dibromo-6,6 -dideoxy-2,3,4,l, 3, 4 -hexa-O-(methylsulfonyl)sucrose and an equimolar mixture of 6- and 6 -bromodeoxysucrose heptakis(methanesulfonates) in 21 and 61% yield, respectively. Unlike the conclusion from previous observations,29,96 presence of the latter product suggested that the reactivities of the 6- and 6 -sulfonyloxy substituents in octa-O-(methylsulfonyl)-sucrose are comparable. The evidence was based only on the results of measurement of the intensity peaks of the H n.m.r. spectra of the... 

A previous Organia Syntheses procedure for the preparation of isocrotonic acid involves the stereospecific Favorskii rearrangement of l,3-dibromo-2-butanone.6 However, the procedure is rather laborious and, in our hands, gives only a modest overall yield of acid. Isocrotonic acid has also been prepared by carbonation of cis-propenyllithium and by sodium amalgam... 

Caution l,3-Dibromo-2-butanone is a powerful lachrymator and a vesicant. This preparation should be carried out in a hood and contact of this compound with the skin should be avoided. 

A. l,3-Dibromo-2-butanone. A mixture of 72.1 g. (90.0 ml., 1.0 mole) of 2-butanone and 100 ml. of precooled (5°) 48% hydrobromic acid is prepared in a 1-1. three-necked round-bottomed flask equipped with a dropping funnel, a condenser (Note 1), and a Teflon stirrer. The flask is immersed in ice water. When the temperature of the mixture reaches 5°, 319.6 g. (102 ml., 2.0 moles) of bromine is added dropwise at a rate such that the temperature does not rise above 10° and unreacted bromine does not accumulate (Note 2). After addition of the bromine is complete, 400 ml. of water is added, and the heavier organic layer is separated and immediately (Note 3) fractionated under reduced pressure (Note 4) through a 25-cm. Widmer column to give pure l,3-dibromo-2-butanone, b.p. 91-94° (13 mm.), n26D 1.5252 (Note 5). The yield is 115-134g. (50-58%) (Note 6). 

B. Isocrotonic Acid. To a solution of 100 g. (1.0 mole) of potassium bicarbonate (Note 7) in 1 1. of water contained in a 2-1. three-necked round-bottomed flask equipped with a condenser, a dropping funnel, and a Teflon stirrer, 46.0 g. (0.2 mole) of l,3-dibromo-2-butanone is added over a 5-minute period... 

The product is l,3-dibromo-2-butanone, on the basis of its observed H NMR spectrum, which showed two signals at low field. One is a two-proton singlet at S 4.6 ppm assignable to CH2Br and the other a one-proton quartet at 8 5.2 ppm assignable to CHBr. 

BromosuHanilamide, 24, 51 1,3-Butadiene, 2,3-dimethyl-, 22,39,40 2-Butanone, 3,4-dibromo-4-phenyl-,... 

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]. 

Alternatively, a,a -dibromo ketones are reductively debrominated with concomitant cyclization by [Cr(C0)4N0][PPN] at -78 or — 95°C in dichloromethane. This method is particularly suited for NMR tube scale experiments, but is limited to tri- and tetrasubstituted cyclopropanones. Bicyclo[1.1.0]butanones are also accessible by this synthetic procedure which utilizes 1,3-elimination of two bromine atoms from 2,4-dibromocyclobutanones. ... 

The dithiolanone was prepared by Luhmann et al. (1977) by treatment of l,3-dibromo-3-methyl-2-butanone with sodium sulfide (together with another cyclization product, the thietanone). 

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