Cyclohexanone pinacol

Photolysis of cyclohexanone also gives rise to a small amount of carbon monoxide, the quantum yield for the process at 3130 A. being 0.02. Photolysis at shorter wavelengths gives rise to high boiling products which are formed by a reaction between the ketone and the substrate. In cyclohexanol solution, cyclohexanone pinacol is formed (40). 

Rearrangement, acid-catalyzed, of cyclohexanone diallyl acetal to 2-allylcyclohexanone, 42,14 of e do-tetrahydrocyclopentadiene to adamantane, 42,9 pinacol, of 1,2-indanediol, 41, 53... 

Because of the many examples of such activation of metal powders by TCS 14 only a limited and arbitrary number will be discussed here. The Clemmensen-type reduction of ketones such as cyclohexanone with Zn powder in the presence of TCS 14 affords, via 2082, 2084, and 2085, cyclohexene and, via 2082, O-silylated pinacol 2083 [19, 20]. Ketones such as 5a-cholestan-3-one 2086 are reduced by Zn dust-TCS 14 in TFIF, in ca 65-70% yield, to give 5a-cholest-2-ene 2087 and ca 5% 5a-cholest-3-ene [21] (Scheme 13.8). 

Preparative scale reduction of cyclohexanone affords principally the tail-to-tail hydrodimer 23 and some of the hcad-to-tail isomer 24 [93]. The proportions vary with pH, and no head-to-head pinacol has been isolated. Both meso- and ( )-forms... 

Addition of LiBr or LiCl to a solution of Sml2 in THF causes a color change from blue to purple. Oxidation potential of Sml2 in THF changes from —1.33 V to —1.98 0.01 V upon addition of I2 or LiBr (more than 1 equiv.), or to —2.11 0.01 V by addition of 12 or more equiv. of LiCl. In the presence of 4-12 equiv. of the bromide or chloride salt, the pinacol coupling reaction of cyclohexanone is accelerated. These salts should be dried before use otherwise, simple reduction to cyclohexanol occurs. The co-existing lithium cation can also act as a Lewis acid to activate the carbonyl group by coordination. ... 

Preparative electrolysis of cyclohexanone17 in solutions containing 0.1 M (C4H9)4NBF4 as the electrolyte were carried out at —2.95 V(SCE), more positive potentials resulted in negligible current. When 0.01 M (DMP)BF4 was added to the solution, electrolysis of cyclohexanone was possible at —2.70 V(SCE). Thus, DMP+ caused a 0.25 V positive shift in the preparative reduction potential of cyclohexanone. DMP + also altered the nature of the product. In the presence of DMP+, cyclohexanone formed only the corresponding pinacol, while in its absence cyclohexanol was the sole product. From this and experiments with other aliphatic ketones (that will be described later) it could be concluded that DMP+ catalyzes the reduction and redirects the... 

Intermolecular Nucleophilic Substitution with Heteroatom Nucleophiles. A patent issued in 1965 claims substitution for fluoride on fluorobenzene-Cr(CO)3 in dimethyl sulfoxide (DMSO) by a long list of nucleophiles including alkoxides (from simple alcohols, cholesterol, ethylene glycol, pinacol, and dihydroxyacetone), carboxylates, amines, and carbanions (from triphenyhnethane, indene, cyclohexanone, acetone, cyclopentadiene, phenylacetylene, acetic acid, and propiolic acid). In the reaction of methoxide with halobenzene-Cr(CO)3, the fluorobenzene complex is ca. 2000 times more reactive than the chlorobenzene complex. The difference is taken as evidence for a rate-limiting attack on the arene ligand followed by fast loss of halide the concentration of the cyclohexadienyl anion complex does not build up. In the reaction of fluorobenzene-Cr(CO)3 with amine nucleophiles, the coordinated aniline product appears rapidly at 25 °C, and a carefiil mechanistic study suggests that the loss of halide is now rate limiting. 

Tetraalkyl- and tetraatyl-ethylene glycols (pinacols) are made by reduction of ketones with active metals such as sodium, magnesium, and aluminum. The reaction is only fair for aliphatic and alicyclic ketones. Acetone, methyl ethyl ketone, cyclopentanone, and cyclohexanone all give less than 0% yields of pinacols. Mixtures of ketones are reduced to unsymmetrical pinacols. An active zinc-copper couple has been employed in the reduction of several simple olefinic aldehydes to dieodiols, e.g., crotonaldehyde to dipropenyl glycol,... 

Ethereal solvents, principally THF, either with or without sonication, have been reported to give results similar to those obtained on reductions in NH3 with no added proton donor, and pinacol formation as a major reaction path. a potentially useful selective reduction of unhindered cyclohexanones in the presence of other ketones using A1 amalgam in aqueous THF has been described and will be discussed in detail subsequently (Section 1.4.3.3.2).2 in this procedure aliphatic ketones give no pinacols however, aromatic ketones give only the corresponding pinacol.2 ... 

The rate of oxidation of diols with lead tetraacetate depends strongly on their configurations cis diols react 200-3000 times faster than trans diols [1154], and the racemates of certain diols react about 15 times faster than the meso forms [1154]. The rates of oxidation of pinacols prepared from cyclopentanone, cyclohexanone, and cycloheptanone are in the ratio... 

In contrast, when the X group is oxygen, the reaction appears to follow the cationic alkene cylization-pinacol-like rearrangement pathway. In this case, reaction of an optically pure acyclic oxygen-containing analog of the system in Scheme 71 leads to a product with preservation of optical activity.This reaction protocol, which accomplishes an overall ring expansion with a tetrahydrofiiran annulation, has been examined for ot-hydroxy-cyclopentanones and -cyclohexanones (Scheme 73 and equations 29-31). ... 

Table 1 Relative Efficacy of Ti" Reagents at the Pinacolic Coupling of Cyclohexanone...

The symmetrical diols derived from cyclopentanone and cyclohexanone can similarly be converted to ring-expanded ketones in good yield. The diols from reductive coupling of cycloheptanone and cy-clooctanone give mainly the corresponding dienes in aqueous acid, especially when heated, but Chris-tol found that pinacol rearrangement is strongly favored even for these materials when cold concentrated sulfuric acid is used as the solvent. 

Uranium. Ephritikhine ha.s established that treatment of either cyclohexanone or benzophenone with UCI4 and Na/Hg affords the pinacol adduct in good yield (Eq. 3.26) [42]. The uranium benzopinacolate intermediate from the homocou-pling of benzophenone was characterized by X-ray crystallography. Mechanistic studies indicate that carbon-carbon bond formation proceeds via ketyl dimerization [43]. 

Dehydroifenatiun. I>iethyl azodicarboxylme has been shown lo elt eci photochemical dehydrogenation of isopropanol to pinacol" and of cyclohexunol lo cyclohexanone. Actually the reagent eifects nonphotochemical oxidation of alcohols, mercaptans, anilines, and hydrazobenzenes with formation of diethyl hydrazinodicarboxylate. ... 

The stereoeontrolled construction of hydroazulenones is achieved by sequential anionic oxy-Cope rearrangement/SN allylic ether displacement of Cope precursors 5 and 7y71. Optically active compounds 5-8 are prepared from (-)-(lR,6S)-A4(10)-caren-rrons-3-ol via intermediates 3 and 4 by individual exposure of 3 and 4 to 3 equivalents of vinylmagnesium bromide. This reagent promotes initial pinacol rearrangement with liberation of a cyclohexanone unit which is captured by a second equivalent of the organometallic. The divinyl alcohol pairs 5/6 and 7/8 are isolated in 2 1 ratios (43-82% combined yields after MPLC). 

The electrochemical properties of many functional groups have been described in reviews by Steckhan, Degner (industrial uses of electrochemistry), Kariv-Miller,543 and Feoktistov. The synthetic applications of anodic electrochemistry has also been reviewed. There are interesting differences between dissolving metal reductions (secs. 4.9.B-G) and electrochemical reactions. Cyclohexanone, for example, can be reduced to cyclohexanol (sec. 4.9.B) or converted to the 1,2-diol (556) via pinacol coupling by controlling the reduction potential, the nature of the electrode and the reaction medium. 46 Presumably, the more concentrated conditions favor formation of cyclohexanol via reduction of the carbanion. More dilute solutions appear to favor the radical with reductive dimerization to 556. More important to this process, however, is the difference in reduction potential (-2.95 vs. -2.700 V) and the transfer of two Faradays per mole in the former reaction and four Faradays per mole in the latter. 

A solution of 1.5 mmol ethyl trimethylsilanylacetate and 2.0 mmol chiral pinacol methyl ether in 6.0 mL toluene was added to a solution of LDA (1.6 mmol) in 5.0 mL toluene at -78°C. The mixture was stirred at -20°C for 1 h and cooled to -78°C again. Then a solution of 1.0 mmol 4-rert-butyl-cyclohexanone in 4 mL toluene was added dropwise over a period of 3 min, and the resulting mixture was stirred at room temperature for 5 h. Upon removal of the solvent, the residue was purified by silica gel column chromatography to afford 68% of (5)-(+)-ethyl (4-tert-butylcyclohexylidene)acetate as a colorless oil, with 19% e.e. 

Ring-expansions have been used in two syntheses of the monoterpene kara-hanaenone (12). In the first, the interest lies in the regioselectivity of the addition of thiophenol to the allene (13) and the rapid Cope rearrangement of the cis-product (Scheme 20), whilst in the second the availability of the pinacolic intermediate relies on the success of the titanium-mediated coupling of acetone with the requisite cyclohexanone [equation (17)]. ... 

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