59214-60-7Relevant articles and documents
Iron-catalyzed pinacol coupling of aryl ketones with a phenyltitanium reagent: A new type of catalytic reaction
Hayashi, Tamio,Sasaki, Keigo
supporting information; experimental part, p. 492 - 494 (2011/06/25)
A reaction of aryl ketones with phenyltitanium triisopropoxide ([PhTi(Oi-Pr)3]) in the presence of [Fe(acac)3] as a catalyst (1 mol%) gave the corresponding pinacols in high yields. The catalytic cycle of this process involves an iron-catalyzed disproportionation of [PhTi(Oi-Pr) 3] into biphenyl and a lowvalent titanium species.
Efficient method for the preparation of pinacols derived from aromatic and aliphatic ketones by using low-valent titanium reagents in dichloromethane-pivalonitrile
Kagayama,Igarashi,Mukaiyama
, p. 657 - 665 (2007/10/03)
The reductive coupling reaction of aldehydes and ketones, including unsymmetrical aliphatic ketones, proceeded smoothly to give the corresponding pinacols in good to high yields under mild conditions by using combination of titanium(II) chloride and zinc or titanium(IV) chloride and zinc in dichloromethane-pivalonitrile. Meso-selective formation of the coupling products was observed in the cases of some aliphatic ketones. The diastereoselectivities of coupling products depend on both difference of bulkiness of 2-, and 2'-substituents of carbonyl group of the reactant, and overall steric effect around the carbonyl groups.
Rate Constants for Degenerate Hydrogen Atom Exchange between α-Hydroxy Radicals and Ketones
Wagner, Peter J.,Zhang, Yuanda,Puchalski, Allen E.
, p. 13368 - 13374 (2007/10/02)
When a phenyl ketone is irradiated in the presence of 1-phenylethanol, the photoproducts include acetophenone pinacol, the pinacol from the other phenyl ketone, a mixed pinacol, and acetophenone, which is formed by irreversible hydrogen atom exchange between the hemipinacol radical of acetophenone and the other ketone.Rate constants for this hydrogen atom exchange between the hemipinacol radical of acetophenone and three other ketones were determined by measuring how acetophenone yields depend on the concentration of the other ketone.Comparable measurements were made for p-chloroacetophenone formation by irradiating acetophenone in the presence of 1-(p-chlorophenyl)ethanol.As the starting ketone concentration increases, so does the amount of exchange relative to pinacol, while the pinacol content reflects decreasing amounts of the original alcohol.Exchange is measurable at ketone concentrations below 0.01 M and is complete by 0.1 M.Rate constants kex of 3.7, 6.3, 4.2, and 8.6 * 103 M-1 s-1 were deduced for hydrogen transfer to propiophenone, isobutyrophenone, p-methylacetophenone, and p-chloroacetophenone, respectively, based on a competing rate constant for radical coupling of 2 * 109 M-1 s-1.Equilibrium constants for the hydrogen transfer were determined from the product ratios obtained by irradiating a mixture of two ketones with 2-propanol; from these k-ex values of 11.5, 57, 13, and 1.8 * 103 M-1 s-1, respectively, were deduced for hydrogen transfer to acetophenone from the four other ketone hemipinacol radicals.These exchange rate constants depend more on the structure of the radical than on that of the ketone.Actual quantum yields for pinacol formation do not exceed 50 percent ; this maximum quantum efficiency rises to 71 percent for 1-phenylethanol-O-d.From this inverse isotope effect it is concluded that half the reaction of triplet acetophenone with 1-phenylethanol involves abstraction of an OH hydrogen followed by disproportionation of the initial radical pair back to reactants.