2039-90-9Relevant articles and documents
Kinetics of α-(2,6-Dimethylphenl)vinyllithium: How to Control Errors Caused by Inefficient Mixing with Pairs of Rapidly Competing Ketones
Knorr, Rudolf,Knittl, Monika,Behringer, Claudia,Ruhdorfer, Jakob,B?hrer, Petra
, p. 2843 - 2854 (2017/03/23)
Kinetic studies are a suitable tool to disclose the role of tiny reagent fractions. The title compound 2 reacted in a kinetic reaction order of 0.5 (square root of its concentration) with an excess of the electrophiles ClSiMe3, 1-bromobutane (n-BuBr), or 1-iodobutane (n-BuI) at 32 °C in Et2O or in hydrocarbon solvents. This revealed that the tiny (NMR-invisible) amount of a deaggregated equilibrium component (presumably monomeric 2) was the reactive species, whereas the disolvated dimer 2 was only indirectly involved as a supply depot. Selectivity data (relative rate constants κobs) were collected from competition experiments with the faster reactions of 2 in THF and the addition reactions of 2 to carbonyl compounds. This provided the rate sequences of Et2C=O > dicyclopropyl ketone > t-Bu-C(=O)-Ph > diisopropyl ketone ? t-Bu2C=O > ClSiMe3 > n-BuI > n-BuBr ≈ (bromomethyl)cyclopropane (but t-Bu2C=O 3 in THF only) and also of cyclopropanecarbaldehyde > acetone ≥ t-Bu-CH=O. It is suggested that a deceivingly depressed selectivity (1 obs A/kB), caused by inefficient microscopic mixing of a reagent X with two competing substrates A and B, may become evident toward zero deviation from the correlation line of the usual inverse (1/T) linear temperature dependence of ln κobs.
A highly active and general catalyst for the stille coupling reaction of unreactive aryl, heteroaryl, and vinyl chlorides under mild conditions
Lee, Dong-Hwan,Qian, Yingjie,Park, Ji-Hoon,Lee, Jong-Suk,Shim, Sang-Eun,Jin, Myung-Jong
supporting information, p. 1729 - 1735 (2013/07/19)
A β-diketiminatophosphane-palladium complex was found to act as an efficient and general catalyst in the Stille coupling reaction of various aryl and heteroaryl chlorides with organostannanes. The results show that this catalytic system allows for the use of less reactive substrates such as deactivated or sterically hindered aryl chlorides. A catalyst loading of 0.5 mol% was sufficient to achieve excellent performance under relatively mild reaction conditions. Furthermore, the scope of catalyst was extended to the coupling of vinyl chlorides. Copyright
Cross coupling in water: Suzuki-Miyaura vinylation and difluorovinylation of arylboronic acids
Pschierer, Jan,Peschek, Natalie,Plenio, Herbert
experimental part, p. 636 - 642 (2010/08/20)
A general and efficient protocol for the Suzuki-Miyaura coupling of aryl boronic acids with vinylmesylate or difluorovinylmesylate or Cl 2CCF2 in water or water/n-butanol is reported, utilizing Na2PdCl4 (1 mol%) and a highly water-soluble fluorenylphosphine (CataCXium F sulf).
Novel anti-Markovnikov regioselectivity in the Wacker reaction of styrenes
Wright, Joseph A.,Gaunt, Matthew J.,Spencer, Jonathan B.
, p. 949 - 955 (2007/10/03)
The Wacker reaction is one of the longest known palladium-catalysed organic transformations, and in the vast majority of cases proceeds with Markovnikov regioselectivity. Palladium(II)-mediated oxidation of styrenes was examined and in the absence of reoxidants was found to proceed in an anti-Markovnikov sense, giving aldehydes. Studies on the mechanism of this unusual transformation were carried out, and indicate the possible involvement of a η4-palladium-styrene complex. With a heteropolyacid as the terminal oxidant, oxidation of styrene to give the anti-Markovnikov aldehyde as the major product was found to be catalytic.
Dimeric α-lithio-2,6-dimethylstyrene
Knorr, Rudolf,Behringer, Claudia,Noeth, Heinrich,Schmidt, Martin,Lattke, Ernst,Raepple, Edith
, p. 585 - 592 (2007/10/03)
Improved preparations of 2,6-dimethylstyrene (5) and its abromo derivative (10) are described. The Br/Li exchange reaction of 10 provides single crystals of the title compounds 11 or 12, which were characterized as disolvated dimers by X-ray analyses. A similar dimer persists in diethyl ether, tertbutyl methyl ether, and toluene at all accessible temperatures, with significant lithiation NMR shifts (relative to 5) partially due to charge delocalization from the sp2-carbanionic center. Some NMR coupling constants are typical of the dimeric aggregate. The configurational (E,Z) lability is quantified in toluene solution. VCH Verlagsgesellschaft mbH.
THE PHENYLCARBENE REARRANGEMENT REVISITED
Gaspar, Peter P.,Hsu, Jong-Pyng,Chari, Sarangan,Jones, Maitland Jr.
, p. 1479 - 1508 (2007/10/02)
The evolution of mechanistic ideas about the phenylcarbene rearrangement has been reviewed, and three closely linked problems have been identified toward whose solution this research has been aimed: 1.Why do the ratios of the stable end products from the rearrangements of o-, m- and p-tolylmethylene differ when all three reactions have been thought to pass through a common intermediate? 2.Why does the rearrangement of 2-methylcycloheptatrienylidene lead to exclusive formation of styrene? 3.What is the mechanism of styrene formation from o-tolylmethylene? New mechanisms have been proposed in which m- and p-tolylmethylene can rearrange to styrene without necessarily being converted to o-tolylmethylene.The formation of a small amount of 2,6-dimethylstyrene from the rearrangement of 3,4,5-trimethylphenylmethylene is viewed as evidence for such a mechanism, and a set of interconverting norcaradienylidenes are believed to be the crucial intermediates.Other alternatives are considered and rejected on the basis of the rearrangement products of 3,5-dimethyl- and 3,4,5-trimethylphenylmethylene.
