2040-01-9Relevant articles and documents
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.
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.
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.
