19689-18-0Relevant articles and documents
Dramatic Concentration Depedence of Stereochemistry in the Wittig Reaction. Examination of the Lithium Salt Effect
Reitz, Allen B.,Nortey, Samuel O.,Jordan, Alfonzo D.,Mutter, Martin S.,Maryanoff, Bruce E.
, p. 3302 - 3308 (1986)
The stereochemistry for Wittig reactions of butylidenetriphenylphosphorane (1) with benzaldehyde and hexanal was examined in detail with regard to concentration effects.For the reaction of 1 and benzaldehyde in the presence of LiBr, the proportion of trans-oxaphosphetane (measured by low-temperature 31P NMR) and (E)-alkene increased with respect to increasing reaction concentration in THF, approaching limiting values in a hyperbolic manner.Stereochemical drift, i.e., exaggerated production of (E)-alkene relative to trans-oxaphosphetane intermediate, was also concentration dependent, being more pronounced at higher concentrations.Experiments with varying amounts of lithium cation, and with NaBr instead of LiBr, demonstrated that this phenomenon is associated with the concentration of Li ion, which is increasingly sequestered by the THF solvent at higher dilution.In Me2SO, the dependence of alkene stereochemistry on concentration was greatly attenuated.In toluene, the concentration effect was inverted to some extent; more (E)-alkene was formed at higher dilution ( no betaines were observed by 31P NMR at low temperature).The reaction of 1 with hexanal in THF, in the presence of LiBr, exhibited a concentration depedence similar to that observed for the reaction with benzaldehyde ( at the oxaphosphetane stage).The rates of the lithium-dependent ("catalyzed") and lithium-independent ("uncatalyzed") reactions in the original carbon-carbon bond-forming step are ranked relative to each other, based on their concentration dependence in THF.For 1 and benzaldehyde in THF (with LiBr present), the catalyzed (k'') and uncatalyzed (k') rates constant have the following relative order: k1'' = 5.2 and k2'' = 2.5 mol-2*dm6*s-1; k1' = 1.0 and k2' -1*dm3*s-1 (see Scheme I and Appendix).Thus, at the representative concentrations of 0.05, 0.20, and 0.50 M, the original carbon-carbon bond-forming step in this Wittig reaction is 27percent, 61percent, and 79percent lithium catalyzed, respectively.
Photocatalytic-controlled olefin isomerization over WO3–x using low-energy photons up to 625 nm
Sun, Xichen,Waclawik, Eric R.,Wang, Yunwei,Zhang, Jin,Zheng, Zhanfeng,Zhu, Pengqi
, p. 1641 - 1647 (2021/06/28)
WO3–x (W-1) was used to achieve controllable photoisomerization of linear olefins without substituents under 625 nm light irradiation. Thermodynamic and kinetic isomers were obtained by regulating the carbon chain length of the olefins. Terminal olefins were converted into isomerized products, and the internal olefin mixtures present in petroleum derivatives were transformed into valuable pure olefin products. Oxygen vacancies (OVs) in W-1 altered the electronic structure of W-1 to improve its light-harvesting ability, which accounted for the high activity of olefin isomerization under light irradiation up to 625 nm. Additionally, OVs on the W-1 surface generated unsaturated W5+ sites that coordinated with olefins for the efficient adsorption and activation of olefins. Mechanistic studies reveal that the in situ formation of surface π-complexes and π-allylic W intermediates originating from the coordination of coordinated unsaturated W5+ sites and olefins ensure high photocatalytic activity and selectivity of W-1 for the photocatalytic isomerization of olefins via a radical mechanism.
Catalytic asymmetric carbong-carbon bond formation via allylic alkylations with organolithium compounds
Perez, Manuel,Fananas-Mastral, Martin,Bos, Pieter H.,Rudolph, Alena,Harutyunyan, Syuzanna R.,Feringa, Ben L.
experimental part, p. 377 - 381 (2012/01/06)
Carbon-carbon bond formation is the basis for the biogenesis of nature's essential molecules. Consequently, it lies at the heart of the chemical sciences. Chiral catalysts have been developed for asymmetric C-C bond formation to yield single enantiomers from several organometallic reagents. Remarkably, for extremely reactive organolithium compounds, which are among the most broadly used reagents in chemical synthesis, a general catalytic methodology for enantioselective C-C formation has proven elusive, until now. Here, we report a copper-based chiral catalytic system that allows carbon-carbon bond formation via allylic alkylation with alkyllithium reagents, with extremely high enantioselectivities and able to tolerate several functional groups. We have found that both the solvent used and the structure of the active chiral catalyst are the most critical factors in achieving successful asymmetric catalysis with alkyllithium reagents. The active form of the chiral catalyst has been identified through spectroscopic studies as a diphosphine copper monoalkyl species.
Liquid phase alkylation of benzene with dec-1-ene catalyzed on supported 12-tungstophosphoric acid
Hernández-Cortez,Martinez,Soto,López,Navarrete,Manríquez,Lara,López-Salinas
scheme or table, p. 346 - 352 (2010/08/06)
The liquid phase alkylation of benzene with dec-1-ene was catalyzed by 12-tungstophosphoric acid (WP) supported on different solids (ZrO2, SiO2, activated carbon and boehmite-Al2O3). Catalysts prepared with 20 w
Synthesis of Farnesol Analogues through Cu(I)-Mediated Displacements of Allylic THP Ethers by Grignard Reagents
Mechelke, Mark F.,Wiemer, David F.
, p. 4821 - 4829 (2007/10/03)
The synthesis of a family of farnesol analogues, incorporating aromatic rings, has been achieved in high yields through the development of a regioselective coupling of allylic tetrahydropyranyl ethers with organometallic reagents. The allylic THP group is displaced readily by Grignard reagents in the presence of Cu(I) halides but is stable in the absence of added copper. Thus, an allylic THP group can fulfill its traditional role as a protecting group or serve as a leaving group depending on reaction conditions. An improved synthesis of (2E,6E)-10,11-dihydrofarnesol also has been accomplished using this methodology, and some preliminary studies on the reactivity and regioselectivity of THP ether displacements were conducted. The farnesol analogues reported herein may be useful probes of the importance of nonbonding interactions in enzymatic recognition of the farnesyl chain and allow development of more potent competitive inhibitors of enzymes such as farnesyl protein transferase.
Organometallic chemistry sans organometallic reagents: Modulated electron-transfer reactions of sub valent early transition metal salts
Eisch, John J.,Shi, Xian,Alila, Joseph R.,Thiele, Sven
, p. 1175 - 1187 (2007/10/03)
The potential of low-valent, early transition-metal reagents as selective reductants in organic chemistry has been foreshadowed by intensive research on the ill-defined and heterogeneous subvalent titanium intermediates generated in the McMurry reaction and its numerous variants. As part of a long-term research effort to develop soluble, well-defined transition-metal reductants of modulated and selective activity toward organic substrates, the THF-soluble reductant, titanium dichloride, has been thoroughly examined, as well as the analogous ZrCl2 and HfCl2 reagents, all of which are readily obtainable by the alkylative reduction of the Group 4 tetrachloride by butyllithium in THF. Noteworthy is that such interactions of MCl4, with butyllithium in hydrocarbon media lead, in contrast, to M(III) or M(IV) halide hydrides. Analogous alkylative reductions in THF applied to VCl4, CrCl3, and MoCl5 have yielded reducing agents similar to those obtained from MCl4 but gradated in their reactivity. Such reductants have proved capable of coupling carbonyl derivatives, benzylic halides, acetylenes and certain olefins in a manner consistent with an oxidative addition involving a two-electron transfer (TET). Such a reaction pathway is consistent with the observed stereochemistry for pinacol formation from ketones and for the reductive dimerization of alkynes. In contrast to the reaction of CrCl3 with two equivalents of butyllithium, which leads to a CrCl intermediate, the interaction of CrCl3 in THF with four equivalents of butyllithium at -78°C yields a reagent of the empirical formulation, LiCrH4 · 2 LiCl · 2 THF, as supported by elemental and gasometric analysis of its protolysis. This hydridic reductant cleaves a wide gamut of o carbon-heteroatom bonds (C-X, C-O, C-S and C-N), towards which the CrCl reductant is unreactive. The type of cleavage and/or coupled products resulting from the action of "LiCrH4" on these substrates is best understood as arising from single-electron transfer (SET). In light of the aforementioned findings, the gradated reducing action noted among TiCl2, ZrCl2, HfCl2 and CrCl, as well as the contrasting reducing behavior between CrCl and LiCrH4, there is no doubt that future research with early transition metals will continue to yield novel reductants of modulated and site-selective reactivity. VCH Verlagsgesellschaft mbH,.
STEREOCHEMICAL OBSERVATIONS ON THE WITTIG REACTION OF OXIDO PHOSPHONIUM YLIDES WITH ALDEHYDES
Maryanoff, Bruce E.,Reitz Allen B.,Duhl-Emswiler, Barbara A.
, p. 2477 - 2480 (2007/10/02)
The reaction of aldehydes with oxido ylides shows a dramatic dependence of alkene stereochemistry on the distance between oxygen and phosphorus atoms; ylides with proximal O and P atoms favor production of E alkenes.The high E stereoselectivity with γ-oxido ylides is not mainly attributable to intramolecular proton-exchange in a Wittig intermediate.
