111662-72-7Relevant articles and documents
Ether formation through reductive coupling of ketones or aldehydes catalyzed by a mesoionic carbene iridium complex
Petronilho,Vivancos,Albrecht
, p. 5766 - 5774 (2017/12/07)
An iridium(iii) Cp? complex containing a triazolylidene-pyridyl C,N-bidentate-coordinating ligand is a very powerful catalyst for the transformation of ketones and aldehydes into symmetrical ethers. This highly efficient reductive coupling proceeds immediately at room temperature and at a low catalyst loading (0.1 mol%) when Ph2SiH2 is used as an additive. Aromatic carbonyl substrates react faster than aliphatic ketones or aldehydes, and the substrate scope suggests some functional group tolerance. Likewise, the condensation of alcohols to symmetrical ethers is catalyzed by this triazolylidene iridium complex, though ether formation is an order of magnitude slower than when starting from the analogous ketone or aldehyde as a substrate, suggesting that alcohols are not potential intermediates in the reductive coupling process. Prolonged reactions or modification of the silane additive lead to ether cleavage and dehydration, thus affording the corresponding olefin. Mechanistic insights and in particular the different reactivities of alcohols and ketones have been exploited to develop a synthetic methodology for the iridium-catalyzed formation of unsymmetrical methyl ethers (R-OMe) in good yields.
Reactions of Substituted 1-Phenylethyl Carbocations with Alcohols and Other Nucleophilic Reagents
Richard, John P.,Jencks, William P.
, p. 1373 - 1383 (2007/10/02)
Selectivities of a series of substituted 1-phenylethyl carbocations toward alcohols and other nucleophiles have been determined by product analysis.The 1-(4-dimethylamino)phenyl)ethyl carbocation exhibits a high selectivity in its reactions with alcohols , with KEtOH/KTFE = 140 and βnuc = 0.5.The selectivity for activation-limited reactions with alcohols decreases progressively with increasing reactivity of the carbocation, in contrast to the behavior expected from the N+ scale of reactivity.A sharper drop in selectivity for carbocations that react faster than ca. 109 S-1 is attributed to an approach to limiting rate constants for the more reactive alcohol.The limiting selectivity of kEtOH/kTFE = 2 for carbocations with ks ca. 1011 S-1 may represent reaction from a pool of solvent molecules in which there is a modest charge-dipole interaction between the alcohol and carbocation.The relatively low reactivity of water corresponds to that expected for an alcohol of pKa ca. 13.This is ascribed to an imbalance between charge development and solvation of the transition state compared with H3O+.Substituted acetate anions react with the 1-(4-methoxyphenyl)ethyl carbocation with βnuc = 0.13.The selectivity decreases with increasing cation reactivity as the carboxylate ions approach limiting rate constants of ca. 5 * 108 M-1 s-1.This relatively low limit is attributed to a requirement for desolvation of basic oxygen anions before reaction.A dependence of solvent selectivity on the leaving group shows that the 1-(4-methylphenyl)ethyl carbocation reacts with solvent, in part, through an ion pair.Azide ion reacts from a pool that can be described by an equilibrium constant of Kas = 0.3 M-1.Styrene formation from this carbocation is catalyzed by a leaving carboxylate ion and by added buffers, wih β = 0.14.The equilibrium constant for the formation of a reactive base-cation pair is ca. 0.04 M-1.Rate constants for collapse of the ion pair, to form ester, and for proton removal, to form 4-methylstyrene, were estimated to be approximately 1.6 * 1010 s-1 and 6 * 107 s-1, respectively.The rate constants for deprotonation and for hydration of the styrene give the acid dissociation constant of the carbocation to form 4-methylstyrene, pKA = -11.2.
