5-Bromo-2-pentanone

In some cases, the Grignard reaction can be performed intramolecularly. For example, treatment of 5-bromo-2-pentanone with magnesium and a small amount of mercuric chloride in THE produced 1-methyl-1-cyclobutanol in 60% yield. Other four- and five-membered ring compounds were also prepared by this procedure. Similar closing of five- and six-membered rings was achieved by treatment of a 6- or s-halocarbonyl compound, not with a metal, but with a dianion derived from nickel... 

An attempt to form a Grignard reagent from 5-bromo-2-pentanone is doomed to failure because the Grignard will react with the carbonyl group. 

In some cases, the Grignard reaction can be performed intramolecularly. For example, treatment of 5-bromo-2-pentanone with magnesium and a small amount... 

Although the reaction of electrophilic cyclopropanes with protonic acids cannot be considered as apparently strictly nucleophilic processes, this reaction can be classified under this section. For example hydrobromination of ethyl 1-acetylcyclopropane carboxylate (674) affords 5-bromo-2-pentanone (675) (equation 238) ... 

Picoline (2-methylpyridine) gives a lithio derivative that with 5-bromo-2-pentanone ethylene ketal affords 6-(2-pyridyl)-2-hexanone ethylene ketal in 80% yield 421... 

A short synthesis of the tetracyclic y-lycorane derivatives (13a) and (13b) from isocarbostyrils has been reported (Scheme 2). N-Alkylation of (11a) and (11b) with 5-bromo-2-pentanone ethylene ketal gave the ketals (12a) and (12b), respectively. Acid hydrolysis provided the corresponding ketones which upon base-catalysed cyclization yielded compounds (13a) and (13b), respectively. 

In a similar way, dl-2-(q-hydroxyalkyl)- and 2-(a-alkoxycarbonyl)-4-methyl-5-(/3-hydroxyethyl)thiazoles were synthetized from the corresponding thioamides and 4-hydroxy-3-bromo-2-pentanone (615). 

A mixture of 22 parts of 1 -ethyl-1,4-dihydro-5H-tetrazol-5-one,45 parts of 1 -bromo-2-chloro-ethane,26 parts of sodium carbonate,0.3 part of potassium iodide and 240 partsof 4-methyl-2 pentanone is stirred and refluxed overnight with water-separator. The reaction mixture is cooled, water is added and the layers are separated. The aqueous phase is extracted three times with dichloromethane. The combined organic phases are dried, filtered and evaporated. The residue is purified by column-chromatography over silica gel using trichloromethane as eluent. The pure fractions are collected and the eluent is evaporated, yielding 28.4 parts (80%) of 1-(2-chloroethyi)-4-ethyl-1,4-dihydro-5H-tetrazol-5-one as a residue. 

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]. 

The reaction of ethyl A-arylcarbamates 3 with l-bromo-3,3-dimethyl-2-buta-none or l-bromo-3-ethyl-3-methyl-2-pentanone 4 in the presence of lithium bis(trimethylsilyl)amide (LiHMDS) results in the one-step synthesis of 3-aryl-5-ferf-butyl-2(3/T)-oxazolones 7 in fair to good yields (Fig. 5.2 Table 5.1, Fig. 5.3). This method is efficient for the preparation of bulky 5-substimted-2(37f)-oxazo-lones. 

Methyl-2-nitrosopropane dimer, 413 1 -Methyl-A8-octahydroquinoline, 111-112 yV-Methyl-A -octahydroquinoline, 111-112 Methyl orthoformate, 47, 54 Methyl orthovalerate, 48 2-Methyl-4-oximino-3-pentanone, 396 1 -(N-Methyl-7V-phenylamino)-2-bromo-propane, 105... 

Synthesis The cyclization of ethyl isocyanate with sodium azide by means of AICI3 in refluxing THF gives 1 -ethyl-1,4-dihydro-5H-tetrazol-5-one, which is alkylated with 1-chloro-2-bromo-ethane in the presence of Na2CC>3 and Kl in refluxing 4-methyl-2-pentanone to afford 1-ethyl-4-(2-chloroethyl)1,4-dihydro-5H-tetrazol-5-one i (Janssen (Janssen), 1978 Janssens et al., 1986 Hopkins, 1981 Kleemann et al., 1999). 

Synthesis (Kleemann et al. 1999, Janssen (Janssen), 1973 Janssen et al. (Janssen), 1973, Stokbroekx et al., 1973, Niemegeers et al., 1974) ) Treatment of 2-oxo-3,3-diphenyl-tetrahydrofuran, synthesized by treatment of diphenyl-acetic acid ethyl ester with ethylene oxide, with HBr(gas) yields bromo derivative i, which is then converted into butyryl chloride derivative ii by means of thionyl chloride in refluxing chloroform. Reaction of derivative ii with dimethylamine in toluene affords dimethyl (tetrahydro-3,3-diphenyl-2-furylidene)ammonium bromide, which is then condensed with 4-(4-chlorophenyl)-4-piperidinol by means of Na2C03 and Kl in refluxing 4-methyl-2-pentanone to provide loperamide. 

A mixture of 6.9 parts 4-bromo-2,2-diphenylbutyronitrile, 5 parts 4-(2-oxo-l-benzimidazolinyl)piperidine, 7.3 parts sodium carbonate, a few crystals of potassium iodide in 160 parts 4-methyl-2-pentanone is stirred and refluxed for 12 hours. After cooling the reaction mixture, 100 parts water is added. 

The photostimulated reaction of 2-bromo-3-f-propoxypyridine (278) and ketone enolate ions in liquid ammonia afforded the substitution products 279, which gave quantitatively the furo[3,2-6]pyridines (280) (equation 173). With 2-pentanone enolate ion, 278... 

As mentioned earlier, stereochemistry is not of great concern in this book. However, certain mechanistic types will show specific stereochemical consequences when acting on chiral molecules. With this in mind, predict the product resulting from the E2 elimination of HBr when the shown isomer of 4-bromo-3-methyl-2-pentanone is treated with sodamide. Show all stereochemistry and explain your answer. 

Methyl cyclopropyl ketone has been prepared from ethyl aceto-acetate and ethylene bromide,6 and by the action of methyl-magnesium bromide on cyclopropyl cyanide.6-7 The procedure described for its preparation from 5-chloro-2-pentanone is similar to that of Zelinsky and Dengin.8 5-Chloro-2-pentanone has been prepared by a number of methods.9 The procedure given is essentially that of Boon 10 and of Forman.11 A similar procedure has been used for the preparation of the corresponding bromo-and iodoketones.10... 

The starting material in the synthesis of 106 (157) was 3-(3,4-dimethoxy-phenyl)propanoyl chloride, which with the aid of diazomethane at — 20°C, was converted to the diazo ketone 108. Treatment of 108 in ether with 48% hydrogen bromide gave 4-bromo-l-(3,4-dimethoxyphenyl)-3-pentanone (109). The bromo ketone 109 was heated in an autoclave with 2-iminotetra-hydropyran hydrochloride in methanolic ammonia and yielded the product 106, identical to the alkaloid cypholophine, in an overall yield of 6%. 

In a more recent approach (Scheme 11), Schin-zer solved the problem of the C4-C5 retro-aldol reaction with Braun s (S)-HYTRA (51) [44] by replacing the keto group in /(-ketoaldehyde 49 with a C=C double bond cf. 52, derived in four steps from ethyl-2-bromo-Ao-butyrate and 3-pentanone in 13% overall yield). The thus formed intermediate 53 is later deprotected and cleaved oxidatively to give the desired C5 ketone 7 in 52 % yield and 96 % ee from aldehyde 52 [22]. 

Ni(C5H4NBr)a(C10a)2] Diper-chloratotetra (3-bromo-pyridine)nickel(II), 9 179 [Ni(C6HgNO)2] Bis(4-imino-2-pentanon ato) nickel (II),... 

Problem 23.15 Draw the organic products fomned when 2-bromo-3-pentanone (CH3CH2COCHBrCH3) is treated with each reagent (a) Li2C03, LiBr, DMF (b) CH3CH2NH2 (c) CH3SH. 

C5H9Br 3-bromo-2-methyl-1 -butene 51872-48-1 376.08" 32.774 2 5067 C5H9CIO 1 -chloro-3-pentanone 32830-97-0 396.53 34.038 2... 

The total synthesis of (-)-denticulatin A, a polypropionate metabolite, was accomplished in the laboratory of F.E. Ziegler. To establish the absolute stereochemistry at C12, they utilized the Enders SAMP/RAMP hydrazone alkylation. To this end, the RAMP hydrazone of 3-pentanone was successfully alkylated with 1-bromo-2-methyl-2( )-pentene. Hydrolysis of the hydrazone under standard acidic conditions led to loss of the enantiomeric purity. This problem was avoided by using cupric acetate for the cleavage. 

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