2040-01-9Relevant academic research and scientific papers
The effect of solubility on the stability of titanium(IV) arene complexes derived from hexasubstituted arenes and TiCl4
Kiprof, Paul,Li, Jun,Renish, Catherine L.,Kalombo, Eddie K.,Young Jr., Victor G.
, p. 113 - 118 (2001)
The investigation of new titaniuni(IV) hexaalkylarene complexes gave new insight into the stability of high-valent metal arene complexes. In contrast to low-valent transition metal arene complexes these complexes are in equilibrium with the free arenes. The stability of the complexes was shown to depend strongly on both the donor ability of the arene and on their solubility. This is unprecedented in transition metal arene chemistry.
Hydrogen-Borrowing Alkylation of 1,2-Amino Alcohols in the Synthesis of Enantioenriched γ-Aminobutyric Acids
Hall, Christopher J. J.,Goundry, William R. F.,Donohoe, Timothy J.
supporting information, p. 6981 - 6985 (2021/03/01)
For the first time we have been able to employ enantiopure 1,2-amino alcohols derived from abundant amino acids in C?C bond-forming hydrogen-borrowing alkylation reactions. These reactions are facilitated by the use of the aryl ketone Ph*COMe. Racemisation of the amine stereocentre during alkylation can be prevented by the use of sub-stoichiometric base and protection of the nitrogen with a sterically hindered triphenylmethane (trityl) or benzyl group. The Ph* and trityl groups are readily cleaved in one pot to give γ-aminobutyric acid (GABA) products as their HCl salts without further purification. Both steps may be performed in sequence without isolation of the hydrogen-borrowing intermediate, removing the need for column chromatography.
Manganese complex-catalysed α-alkylation of ketones with secondary alcohols enables the synthesis of β-branched carbonyl compounds
Waiba, Satyadeep,Jana, Sayan K.,Jati, Ayan,Jana, Akash,Maji, Biplab
supporting information, p. 8376 - 8379 (2020/08/13)
Herein, β-branched carbonyl compounds were synthesised via the α-alkylation of ketones with secondary alcohols under "borrowing hydrogen"catalysis. A wide range of secondary alcohols, including various cyclic, acyclic, symmetrical, and unsymmetrical alcohols, have been successfully applied under the developed reaction conditions. A manganese(i) complex bearing a phosphine-free multifunctional ligand catalysed the reaction and produced water as the sole byproduct.
Chemo- A nd Regioselective Synthesis of Acyl-Cyclohexenes by a Tandem Acceptorless Dehydrogenation-[1,5]-Hydride Shift Cascade
Armstrong, Roly J.,Donohoe, Timothy J.,Matheau-Raven, Daniel,Smith, Lewis B.
supporting information, (2020/02/13)
An atom-economical methodology to access substituted acyl-cyclohexenes from pentamethylacetophenone and 1,5-diols is described. This process is catalyzed by an iridium(I) catalyst in conjunction with a bulky electron rich phosphine ligand (CataCXium A) which favors acceptorless dehydrogenation over conjugate reduction to the corresponding cyclohexane. The reaction produces water and hydrogen gas as the sole byproducts and a wide range of functionalized acyl-cyclohexene products can be synthesized using this method in very high yields. A series of control experiments were carried out, which revealed that the process is initiated by acceptorless dehydrogenation of the diol followed by a redox-neutral cascade process, which is independent of the iridium catalyst. Deuterium labeling studies established that the key step of this cascade involves a novel base-mediated [1,5]-hydride shift. The cyclohexenyl ketone products could readily be cleaved under mildly acidic conditions to access a range of valuable substituted cyclohexene derivatives.
Direct Synthesis of Cycloalkanes from Diols and Secondary Alcohols or Ketones Using a Homogeneous Manganese Catalyst
Kaithal, Akash,Gracia, Lisa-Lou,Camp, Clément,Quadrelli, Elsje Alessandra,Leitner, Walter
supporting information, (2019/11/21)
A method for the synthesis of substituted cycloalkanes was developed using diols and secondary alcohols or ketones via a cascade hydrogen borrowing sequence. A non-noble and air-stable manganese catalyst (2 mol %) was used to perform this transformation. Various substituted 1,5-pentanediols (3-4 equiv) and substituted secondary alcohols (1 equiv) were investigated to prepare a collection of substituted cyclohexanes in a diastereoselective fashion. Similarly, cyclopentane, cyclohexane, and cycloheptane rings were constructed from substituted 1,4-butanediol, 1,5-pentanediol, and 1,6-hexanediol, and sterically hindered ketones following a (4 + 1), (5 + 1), and (6 + 1) strategy, respectively. This reaction provides an atom economic methodology to construct two C-C bonds at a single carbon center generating high-value cycloalkanes from readily available alcohols as feedstock using an earth-abundant metal catalyst.
Catalytic Asymmetric Synthesis of Cyclohexanes by Hydrogen Borrowing Annulations
Armstrong, Roly J.,Akhtar, Wasim M.,Young, Tom A.,Duarte, Fernanda,Donohoe, Timothy J.
supporting information, p. 12558 - 12562 (2019/08/16)
Hydrogen borrowing catalysis serves as a powerful alternative to enolate alkylation, enabling the direct coupling of ketones with unactivated alcohols. However, to date, methods that enable control over the absolute stereochemical outcome of such a process have remained elusive. Here we report a catalytic asymmetric method for the synthesis of enantioenriched cyclohexanes from 1,5-diols via hydrogen borrowing catalysis. This reaction is mediated by the addition of a chiral iridium(I) complex, which is able to impart high levels of enantioselectivity upon the process. A series of enantioenriched cyclohexanes have been prepared and the mode of enantioinduction has been probed by a combination of experimental and DFT studies.
Stereoselective synthesis of alicyclic ketones: A hydrogen borrowing approach
Armstrong, Roly J.,Akhtar, Wasim M.,Frost, James R.,Christensen, Kirsten E.,Stevenson, Neil G.,Donohoe, Timothy J.
supporting information, (2019/11/13)
A highly diastereoselective annulation strategy for the synthesis of alicyclic ketones from diols and pentamethylacetophenone is described. This process is mediated by a commercially available iridium(III) catalyst, and provides efficient access to a wide range of cyclopentane and cyclohexane products with high levels of stereoselectivity. The origins of diastereoselectivity in the annulation reaction have been explored by a series of control experiments, which provides an explanation for how each stereocentre around the newly forged ring is controlled.
Stereoselective Synthesis of Cyclohexanes via an Iridium Catalyzed (5 + 1) Annulation Strategy
Akhtar, Wasim M.,Armstrong, Roly J.,Frost, James R.,Stevenson, Neil G.,Donohoe, Timothy J.
supporting information, p. 11916 - 11920 (2018/09/27)
An iridium catalyzed method for the synthesis of functionalized cyclohexanes from methyl ketones and 1,5-diols is described. This process operates by two sequential hydrogen borrowing reactions, providing direct access to multisubstituted cyclic products with high levels of stereocontrol. This methodology represents a novel (5 + 1) strategy for the stereoselective construction of the cyclohexane core.
Isolation, X-ray structures, and electronic spectra of reactive intermediates in Friedel-Crafts acylations
Davlieva,Lindeman,Neretin,Kochi
, p. 4013 - 4021 (2007/10/03)
Reactive intermediates in the Friedel-Crafts acylation of aromatic donors are scrutinized upon their successful isolation and X-ray crystallography at very low temperatures. Detailed analyses of the X-ray parameters for the [1:1] complexes of different al
A "Hard/Soft" Mismatch Enables Catalytic Friedel-Crafts Acylations
Fuerstner, Alois,Voigtlaender, David,Schrader, Wolfgang,Giebel, Dirk,Reetz, Manfred T.
, p. 417 - 420 (2007/10/03)
(Equation Presented) Cationic complexes of Pt(II) and other late transition metals efficiently catalyze Friedel-Crafts acylations of moderately activated arenes by carboxylic acid anhydrides. The nature of the catalytically relevant species formed from (PhCN)2PtCl2 and AgSbF6 and their interactions with the substrates are studied by NMR and ESI-MS.
