Pinacolone, preparation

To meet the needs of the advanced students, preparations have now been included to illustrate, for example, reduction by lithium aluminium hydride and by the Meerwein-Ponndorf-Verley method, oxidation by selenium dioxide and by periodate, the Michael, Hoesch, Leuckart and Doebner-Miller Reactions, the Knorr pyrrole and the Hantzsch collidine syntheses, various Free Radical reactions, the Pinacol-Pinacolone, Beckmann and Arbusov Rearrangements, and the Bart and the Meyer Reactions, together with many others. 

The pinacolone may be employed for the preparation of trimethylacetlc acid (plvallc acid) by oxidation with sodium hypobromite solution ... 

Methyl /-butyl ketone [1634-04-4] (pinacolone) has been prepared in 74% yield by reaction of / f/-amyl alcohol with formaldehyde in the presence of strong acid catalyst (78,79). 

Other Rea.ctlons, The anhydride of neopentanoic acid, neopentanoyl anhydride [1538-75-6] can be made by the reaction of neopentanoic acid with acetic anhydride (25). The reaction of neopentanoic acid with acetone using various catalysts, such as titanium dioxide (26) or 2irconium oxide (27), gives 3,3-dimethyl-2-butanone [75-97-8] commonly referred to as pinacolone. Other routes to pinacolone include the reaction of pivaloyl chloride [3282-30-2] with Grignard reagents (28) and the condensation of neopentanoic acid with acetic acid using a rare-earth oxide catalyst (29). Amides of neopentanoic acid can be prepared direcdy from the acid, from the acid chloride, or from esters, using primary or secondary amines. 

The general plan of Organic Syntheses has been discussed in the prefaces of the previous volumes. In this volume are published two distinctly different methods of preparation for each of two compounds. The directions for producing /3-chloro-propionic acid first from acrolein and second from trimethylene chlorohydrin, and for producing trimethylacetic acid first from terJ-butyl chloride and second from pinacolone, have been included. This has been deemed advisable since in some countries one raw material is more readily available than the other. 

Scholl et al (Refs 3 4) prepared the same compds by treating ketoximes (such as pina-colone) with nitrogen tetroxide, but he assigned them the structure R2C=N-N02 and called them nitrimines. One of the compds described by him in Ref 4, p 27 is a weak expl. It is the Ag salt of pinacolone-nitraminic acid which puffs off on rapid heating (this compd described below under List of Nitrimines ). Further work on... 

A catalytic amount (5-20 mol %) of the reagent, along with BH3 as the reductant, can reduce ketones such as acetophenone and pinacolone in more than 95% e.e. An adduct of borane and 18 is the active reductant. This adduct can be prepared, stored,... 

Dienones of this class are useful starting materials for the preparation of bicyclic compounds via Diels-Alder reactions1 4 and for the synthesis of small ring compounds.6 The 2,4-dienone can be converted quantitatively to the 2,5-isomer by treatment with fuming sulfuric acid and subsequent hydrolysis.6 The oxidation procedure is also applicable to the conversion of mesity-lene to mesitol or of isodurene to isodurenol,7 and can be used to convert tetramethyl ethylene quantitatively and directly to pinacolone.8... 

Horeau and co-workers (130) found that an ether solution containing four molar equivalents of (+ )-camphor added to one molar equivalent of LAH, followed by addition of A1C13, reduced 2-butanone or pinacolone. The reagent involved is presumably the same as that prepared by Eliel and Nasipuri (111), although the reaction leading to the formation of 111 is different (eq. [29]). The... 

Although acetone is used widely as an industrial solvent, nevertheless it has become the by-product of the acetone-butanol fermentation and there is always the fear of overproduction. There is thus a need for an extension of the industrial utilization of acetone. A possibility in this direction may be in its conversion into pinacol, the preparation of which has recently been improved by McHenry, Drum and O Connor. It is obtained together with isopropyl alcohol by electrolytic reduction of acetone under controlled conditions. Pinacol (LXVI) may be dehydrated to 2,3-dimethylbutadiene which can be converted into a synthetic rubber, or converted through pinacolone (LXVII) into neohexane... 

An extension of the above preparative method of chirality transfer is the preparation of dioxolanes 16 from lactic acid and 3,3-dimelhyl-2-butanone (pinacolone)80. In this case the crude cis/trans ratio is already 95 5, thus, it is much better than the observed 80 20 ratio observed with trimethylacetaldehyde. Alkylation of 16 with benzyl bromide seems to proceed with a satisfactory 95 5 selectivity. 

No. Pinacolone has a trimethylated a C. Acetoacetic ester is used for preparing mono- or dialkylated methyl ketones. The compound is made by a pinacol-pinacolone rearrangement of (CH,)2COHCOH(CH,)2. 

Dehydration of diols pinacol rearrangement. Preparation of pinacolone... 

Prepared from MoCMacac and (Bu Sn O. m Traces of 1,2-diol and pinacolone. 

An attempt to prepare 2-(2-nitrophenyl)-4,6-diphenylpyrylium from l,3-diphenylprop-2-en-1 -one and 2-nitroacetophenone gave only 2,4,6-triphenylpyrylium (58BSF1458). Similarly, substantial formation of this symmetrical pyrylium salt was observed during syntheses of unsymmetrically substituted salts. Thus, pinacolone and chalcone afforded both 2-f-butyl-4,6-diphenylpyrylium and the 2,4,6-triphenyl derivative. The latter product is considered to arise from a retro-aldol reaction of the enone into a mixture of benzaldehyde and acetophenone the latter reacts with unchanged chalcone to give the unrequired salt (80T679). 

In the reaction of the hydroxy ester (87) with methylmagnesium iodide the process stops at the ketone (91) stage. The pinacols were investigated under various pinacolone rearrangement conditions.144 By a Grignard reaction of 2-cyanoquinuclidine (92), 2-benzoyl-quinuclidine (93) has been prepared.49... 

Yamamoto has recently described a novel catalytic, asymmetric aldol addition reaction of enol stannanes 19 and 21 with aldehydes (Eqs. 8B2.6 and 8B2.7) [14]. The stannyl ketones are prepared solvent-free by treatment of the corresponding enol acetates with tributyltin methoxide. Although, in general, these enolates are known to exist as mixtures of C- and 0-bound tautomers, it is reported that the mixture may be utilized in the catalytic process. The complexes Yamamoto utilized in this unprecedented process are noteworthy in their novelty as catalysts for catalytic C-C bond-forming reactions. The active complex is generated upon treatment of Ag(OTf) with (R)-BINAP in THF. Under optimal conditions, 10 mol % catalyst 20 effects the addition of enol stannanes with benzaldehyde, hydrocinnamaldehyde, or cinnamaldehyde to give the adducts of acetone, rerf-butyl methyl ketone (pinacolone), and acetophenone in good yields and 41-95% ee (Table 8B2.3). 

Benzalpinacolone has been prepared only by the action of benzaldehyde on pinacolone in the presence of aqueous alcoholic alkalies. The method described above is a modification 1 of the original method devised by Vorlander and Kalkow.2... 

Pinacolone has been prepared by heating pinacol hydrate with dilute sulfuric acid or dilute hydrochloric acid 1 by treating anhydrous pinacol2 with concentrated sulfuric acid at o° by heating pinacol with 5 per cent oxalic acid 3 for twelve hours, or with 50 per cent tartaric, phosphoric, or oxalic acid 3 for three to four hours. 

The dehydration of ditertiary alcohols in the presence of hydrobromic acid may lead to dienes (e.g. pinacol to 2,3-dimethylbuta- 1,3-diene, cognate preparation in Expt 5.12), although in this case some concomitant rearrangement to t-butyl methyl ketone (pinacolone, Expt 5.98) occurs under the acidic conditions employed. 

In the examples given the preparative value depends upon the ready availability of the required methyl ketone thus pinacolone (Expt 5.98), cyclopropyl methyl ketone (Expt 7.1) and mesityl oxide (Expt 5.213) are converted into 2,2-dimeth-ylpropanoic acid, cyclopropanecarboxylic acid and 3,3-dimethylacrylic acid respectively (Expts 5.124 and 5.125). 

Further examination of the fluoride ion-catalyzed asymmetric aldol reaction of the enol silyl ethers prepared from acetophenones and pinacolone with benzaldehyde using 4b and its pseudoenantiomer 4c revealed the dependence of the stereochemistry of the reactions on the hydroxymethyl-quinudidine fragment of the catalyst (Table 9.3) [10,15]. 

Cleavage of ketones by oxidation is infrequently used for preparation of monocarboxylic acids. Trimethylacetic acid is made in 75% yield from pinacolone, (CHj)jCCOCHj, by oxidation with chromic anhydride in aqueous acetic acid. Cleavage on only one side of the carbonyl group is possible in this case. 

The tributyltin enolates 74 are readily prepared from the corresponding enol acetates and tributyltin methoxide in the absence of solvent [34]. The tin enolates thus obtained occur in the 0-Sn form and/or the C-Sn form, and both species can be used for the aldol reaction of this system. Although the tin enolates themselves have adequate reactivity toward aldehydes [34c], in the presence of the BINAP silver(I) catalyst the reaction proceeds much faster even at -20 °C. Optimum conditions entail the use of THF as solvent and the results employing these conditions in the catalytic enan-tioselective aldol reaction of a variety of tributyltin enolates with typical aromatic, a,/3-unsaturated, and aliphatic aldehydes are summarized in Table 2. TTie characteristic features are (i) All reactions proceed to furnish the corresponding aldol adducts 75 in moderate to high yield in the presence of 10 mol % (i )-BINAP AgOTf complex at -20 °C for 8 h, and no dehydrated aldol adduct is observed (ii) with an a,j3-unsaturated aldehyde, the 1,2-addition reaction takes place exclusively (entry 3) (iii) a bulky alkyl substituent of tin enolate increases the enantioselectivity of the aldol reaction. For instance, the highest ee (95 % ee) is obtained when the tin enolate prepared from pinacolone 77 or rert-butyl ethyl ketone 79 is added to aldehydes (entries 2, 7, and 8) (iv) addition of the cyclohexanone-derived enol tributylstannane 78 (( )-... 

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