Pinacolone, structure

Dihydrochloride, C HjjCIjNjO, Crystals from ethanol, dec 272-275. Soluble in water-Note Formerly a pinacolone structure was assigned to ampheoone B l,2-Bis[p-aminophenylJ-2-methyl-Tpro-... 

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... 

The pinacol rearrangement is a dehydration of an alcohol that results in an unexpected product. When hot sulfuric acid is added to an alcohol, the expected product of dehydration is an alkene. However, if the alcohol is a vicinal diol, the product will be a ketone or aldehyde. The reaction follows the mechanism shown, below. The first hydroxyl group is protonated and removed by the acid to form a carboca-tion in an expected dehydration step. Now, a methyl group may move to fonn an even more stable carbocation. This new carbocation exhibits resonance as shown. Resonance Structure 2 is favored because all tire atoms have an octet of electrons. The water deprotonates Resonance Structure 2, forming pinacolone and regenerating the acid catalyst. 

D. Seebach, Structure and Reactivity of Lithium Enolates. From Pinacolone to Selective C-Alkylations of Peptides. Difficulties and Opportunities Afforded by Complex Structures, Angew. Chem. Int. Ed. Engl 1988, 27, 1624-1654. 

D. Seebach, Structure and reactivity of lithium enolates From pinacolone to selective C-alkyla-tions of peptides. Difficulties and opportunities afforded by complex structures, Angew. Chem., Int. Ed. Engl. 1988, 27,1624. 

Deviations from the Bronsted lines were observed for iodination of several ketones (acetone, diethyl ketone, isopropyl methyl ketone, pinacolone and cyclohexanone) (Feather and Gold, 1965) and for dedeuteration of [2-2H] isobutyraldehyde (Hine et al., 1965) when these reactions are catalysed by pyridines with one or two methyl substituents in the 2- and 6-position. They were ascribed to steric hindrance since their magnitude depends on the structure of the ketone (the deviations increase along the series from acetone to isopropyl methyl ketone to pinacolone) and on the number of a- methyl substituents in the base. It was at first suggested that such steric effects favour a tram coplanar arrangement of the C=0 bond and of the C(a)—H bond at the... 

Seebach, Dunitz and coworkers reported, in 1981226, the first crystal structures of lithium enolates of simple ketones, obtained in THF from pinacolone (3,3-dimethyl-2-butanone) and cyclopentanone. Both were arranged as tetrasolvated cubic tetramers, one THF molecule capping each lithium cation (Scheme 58A). Note that pinacolone enolate can also be crystallized, from heptane at — 20 °C, as a prismatic unsolvated hexamer exhibiting an approximate S6 symmetry and six slight it-cation interactions227,228 (Scheme 58B) or as a dimer in the presence of 2 molecules of TriMEDA29. Similarly,... 

Mixed-metal enolate has also been found. The core of the lithium sodium enolate of pinacolone forms an open stack structure in which two edges of the face-sharing cubes are absent. 

A triple anion complex containing enolate, amide, and halide functionalities can be isolated from the mixture of n-butyl bromide, hexamethyldisilazane, TMEDA, Bu Li and pinacolone (Bu COMe). The resulting solution of LiBr, LiN(SiMc3)2, LiOC(Bu )=CH2, and TMEDA produces crystals of Li4(/.t4-Br)( u-OC(Bu )=CH2)2(M-N(SiMe3)2)(TMEDA)2, which, instead of forming a ladder-type structure, consists of a planar butterfly of four lithium atoms bonded to a //4-Br the stability of this arrangement has been studied with semi-empirical (PM3) and ab initio HE/ LANL2DZ computations. ... 

Exactly 10 years after the previous statement appeared, the first lithium enolate crystal structures were published as (5) and (6). Thus, structural information derived from X-ray diffraction analysis proved the tetrameric, cubic geometry for the THF-solvated, lithium enolates derived from r-butyl methyl ketone (pinacolone) and from cyclopentanone. Hence, the tetrameric aggregate characterized previously by NMR as (7) was now defined unambiguously. Moreover, the general tetrameric aggregate (7) now became embellished in (5) and (6) by the inclusion of coordinating solvent molecules, i.e. THE. A representative quotation from this 1981 crystal structure analysis is given below. 

The pinacolone enolate residue crystallizes as a dimer with solvation by N,lV,lV -trimethylethylene-diamine (TriMEDA) as indicated in formula (141). In this structure the NH hydrogen on the secondary amine is relatively close to the terminal carbon of the enolate residue, i.e. NH—C=C is 2.60 A. This... 

R. Fittig, Justus Liebigs Ann. Chem., 1860, 114, 54. The structure of pinacol (hy ate) was a matter of controversy pinacolone was clearly formed in this work, as judged by descriptions of the odor, b.p., and C, H analysis (the analysis gave correct percentages, but the resultant formula was in error because atomic weights C = 6 and 0 = 8 were used). 

The facile reactions of TiCl3(OPr ), with a variety of O and N donors gave octahedral adducts.392 In the case of pinacolone (OC(Me)(But)) a 1 2 adduct was formed and exchange of free and bound pinacolone was shown to proceed via a dissociative mechanism. An X-ray crystal structure established the dimeric nature of (M iCl2(//-Cl)(0C(Me)(But)))2()7-02C6I IyMe) (42).393 Other dimeric derivatives of TiCl3(OPr ) have also been described.94,3... 

The thermal stability of the Mg aldolates is most probably a consequence of the strong chelation of fhe carbonyl function with the highly Lewis acidic metal within their dimeric structures. The molecular structure of fhe amide/aldolate derived from fhe selfcoupled aldol reaction between pinacolone and [(Me3Si)2N]2Mg has been reported [26]. 

The yield of the product carbonyl compounds can be very high if suitable experimental conditions are applied. The catalyst of choice under homogeneous conditions is sulfuric acid, either dilute or concentrated this enables the synthesis of pinacolone in almost quantitative yield [11]. Even when selective rearrangement occurs, however, a complex mixture of rearrangement products might be formed, depending on the structure of the starting compound. For example, diol 3 or any... 

Lithium enolates of ketones exist as aggregates in solution.29-3l,34d,35 Mixed aggregates between the enolate anion and the amide base are also possible. In 1981, Seebach and co-workers confirmed by X-ray crystallography that the lithium enolates of pinacolone and cyclopentanone form a tetrameric aggregate in the solid state, and it was assumed that a similar species exited in solution. A THF solvated tetramer of lithium pinacolonate is shown (see 33), as it was reported by Seebach. Williard et al. reported the X-ray structure of... 

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