3- Pentanone preparation

Show how each of the following compounds could be prepared from 3 pentanone In most cases more than one synthetic transformation will be necessary... 

Acetonide formation is the most commonly used protection for 1,2- and 1,3-diols. The acetonide has been used extensively in carbohydrate chemistiy to mask selectively the hydroxyls of the many different sugars. In preparing acetonides of triols, the 1,2-derivative is generally favored over the 1,3-derivative, but the extent to which the 1,2-acetonide is favored is dependent on stmcture. Note that the 1,2-selectivity for the ketal from 3-pentanone is better than that from acetone. ... 

Mimk and Kim (60) have reported the preparation of the enamines of several acyclic ketones by refluxing the ketone with the amine for 66 hr to 76 days. For example the morpholine enamine of 2-pentanone was found to consist only of 121. 

How would you prepare 2-methyl-3-pentanone from a nitrile ... 

Problem 22.5 1 Show how you might prepare 1-pen ten-3-one from 3-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... 

The less highly substituted Mannich bases can also be prepared directly from ketones and dimethyl(methylene)ammonium trifluoroacetate by the procedure reported here, which takes advantage of the isomerization of Mannich bases in trifluoroacetic acid. (In acetic acid the Mannich bases undergo elimination of dimethylamine to give a-methylene ketones.) This method is rapid and affords products having an isomeric purity of at least 90% without difficult separations. The 49-57% yield of l-(di-methylamino)-4-methyl-3-pentanone obtained with this procedure compares favorably with the overall yields of amino ketones prepared by the indirect routes mentioned previously. 

The reduction of nitro ketones with baker s yeast is a good method for the preparation of chiral nitro alcohols.89 The reduction of 5-nitro-2-pentanone with baker s yeast gives the corresponding (5)-alcohol, which is an important chiral building block. Various chiral natural products are prepared from it. In Scheme 7.16, the synthesis of the pheromone of Andrena haemorrhoa is described, where the acylation of the chiral nitro alcohol followed by radical denitration is involved as key steps.89a... 

A good example of applying the hydrazone method is the preparation of the optically active pheromone 34 (Scheme 2-22).38 Further study of the crude product prepared from SAMP-hydrazone and 3-pentanone 33 shows that, among the four possible stereoisomers, (Z,S, S )-isomer 35 predominates along with the minor (E,S,S)-isomer, the geometric isomer of 35. The final product 34 was obtained with over 97% enantiomeric excess (ee). 

The submitter prepared the material from dimethyl adipate following the procedure published by Pickney for the diethyl ester. The checkers obtained their material by fractional distillation of mixed carbomethoxy- and carbethoxycyclo-pentanone available from Arapahoe Chemical Co., Boulder, Colorado. 

In another approach, several ct-hydroxydimethylacetals 258, available according to Scheme la, undergo bimolecular loss of MeOH under acid catalyst, to yield the corresponding 1,4-dioxanes 259 (84JOC4581) (Eq. 42). In the case of 3,3-dimethoxy-2-pentanol (260), which is prepared from 3-pentanone, the cyclization gives dioxane 261 rather than the expected 262 (Scheme 65). The rearrangement of 260 to a mechanistically reasonable precursor of 261 is well known from the work of Creary and Rollin (77JOC4231). 

Furthermore, this reaction was applied to the aldol reaction of 3-pentanone. When the chiral oxazolidine was prepared from 3-pentanone and the aldol reaction was carried out by the same procedure, the a, 6-anti 6-hydroxy ketones were produced predominantly over the syn-isomer 8i with excellent optical purities.(5) (See Table 2.)... 

Prepare 2 solutions as follows - (A) Dissolve 5 parts N-f4-piperidyl) propionanilide, 6.85 parts sodium carbonate, 0.05 parts potassium iodide in 120 parts hexane. (B) Dissolve 3.8 parts B-phenylethylchloride in 24 parts 4-methyl-2-pentanone. 

A similar acetylation procedure (without p-toluenesulfonic acid) has been employed to prepare other /3-diketones.5 As examples, cyclohexanone was converted to 2-acetylcyclohex-anone (73%) cyclopentanone yielded 2-acetylcyclopentanone (80%) 3-pentanone yielded 3-methyl-2,4-hexanedione (81%) dibenzyl ketone yielded l,3-diphenyl-2,4-pentanedione (72%), and acetophenone gave benzoylacetone (70%). 

Oxidation of cyclic ketones by H2O2 in the presence of an acid zeolite was used for the preparation of lactones and u-hydroxycarboxylic acids [124]. Thus, for c-pentanone oxidation in the presence of H-ZSM-5, -valerolactone is obtained with 62.3% selectivity at 40% conversion, whereas 5-hydroxy-pentoic acid is obtained with 34% yield in the presence of Zeolon M. 

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. 

The configuration of the Claisen rearrangement product (J )-( )-2,4-dimethyl-4-heptenoic acid (see p 422)144 was determined by correlation with a reference sample of (f )-4,6-dimethyl-6-nonen-3-one (1) prepared from 3-pentanone employing the RAMP-hydrazone method221. Configurational assignment thus rests on the well-established stereochemical course of the Enders method 222. 

In the case of 3-pentanone, evidence has been presented27-28 for thermodynamic control during formation of the (Z)-enolates and for kinetic control during formation of the ( )-eno-lates in the presence or absence of HMPA. Ester enolates are preferentially ( ), when prepared with LDA (THF), and (Z) when prepared with LDA in the presence of HMPA. In contrast, dialkylamides are deprotonated (LDA/THF) preferentially to give the (Z)-enolates. The role of HMPA in the above case is still not quite clear6-29. 

As is shown in Scheme 1.2.28, our retrosynthehc analysis led us to the ketodiol 127, providing access to the target pheromone after intramolecular acetalization. It was planned to prepare the dihydroxyketone 127 by diastereoselective ring opening of the epoxide 128 with either enantiomerically pure 3-pentanone SAMP... 

The title compound is prepared by condensation of citral (see p.36) with 2-pentanone in the presence of bases to give 8,12-dimethyltrideca-5,7,l l-trien-4-one, which is cyclized and hydrogenated [113]. 

Problem 17.17 Prepare 3-methyl-2-pentanone from acetoacetic ester. In the product... 

Preparation of 2-Methyl-2-nitroso-3-pentanone Dimer and 2-Methyl-4-oximino-3-pentanone [35]... 

This procedure is essentially that reported previously,5 4,6-Dimethyl-l-hepten-4-ol has also been prepared by the reaction between allylmagnesium bromide and 4-methyl-2-pentanone,4 by the treatment of magnesium with a mixture of allyl bromide and... 

During a preparation of the complex [Ni(NCS)2 P(CH2CH2CN)3 2] in acetone solution, a yellow-orange compound was obtained which was characterized as [Ni(C6H1202)2][Ni(NCS)4- P(CH2CH2CN)3 2] (152) (Cdiacetone alcohol ). This reaction, which involves an aldol condensation of two acetone molecules, was found to be not reproducible. 11858,1185b... 

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