81390-14-9Relevant articles and documents
Key role of Ti(IV) in the selective radical - radical cross-coupling mediated by the ingold-Fischer effect
Spaccini, Raffaele,Pastori, Nadia,Clerici, Angelo,Punta, Carlo,Porta, Ombretta
supporting information; experimental part, p. 18018 - 18024 (2009/06/28)
We report an innovative approach for the selective synthesis of polyfunctional derivatives by cross-combination of different radicals generated under mild conditions. The coordinating effect of Ti(IV) plays a key role in the reaction mechanism: due to its chelating action on the hydroxyl groups, it promotes the homolytic C-C bond cleavage of α,β-dihydroxy ketones by enhancing the captodative effect and the consequent stabilization of the corresponding α-hydroxy-α-carbonyl radicals. When these radicals are generated in the presence of stoichiometric amounts of TiCl4 and 2,2'-azo-bis-isobutyronitrile (AIBN) is employed as a source of α-cyanoisopropyl radicals, the selective radical-radical cross-coupling is observed, affording the corresponding β-hydroxynitriles in high yields. This innovative methodology allows application of the well-known Ingold-Fischer effect to a wider range of stabilized carbon-centered radicals, whose formation derives from the chelating action of Ti(IV).
Reactivity of methyl mandelate-Ti(IV)-enediolate: Oxidative homocoupling versus aldol and direct Mannich-type syn-diastereoselective condensation
Clerici, Angelo,Pastori, Nadia,Porta, Ombretta
, p. 4174 - 4176 (2007/10/03)
Methyl mandelate undergoes quantitative oxidative homocoupling on treatment with TiCl4/amine at room temperature. In the presence of ArCHO, quantitative syn-diastereo-selective aldol condensation takes over the dimerization, whereas exclusive M
Efficient diastereoselective synthesis of α,β-dihydroxyesters from methyl phenylglyoxylate and aldehydes mediated by titanium trichloride/pyridine system
Clerici,Clerici,Malpezzi,Porta
, p. 13385 - 13400 (2007/10/02)
The reductive coupling of methyl phenylglyoxylate 2 with aliphatic and aromatic aldehydes 3, promoted by TiCl3/Py system in anhydrous THF, affords α,β-dihydroxyesters 4 in good yields (60-94%) and high syn-diastereoselectivity (up to 85%). The type of ligand at the metal ion necessary to achieve a high level of diastereocontrol and the possible mechanism involved are discussed.
Solvent Effect in the Reduction of α-Keto Esters by Aqueous Titanium Trichloride
Clerici, Angelo,Porta, Ombretta
, p. 5099 - 5104 (2007/10/02)
In the reduction of 1 by Ti(III) ion the dimeric 3 or monomeric 4 reduction products could be made to predominate by the choice of the solvent.It is found that (a) dimerization, via coupling of two radicals 2, increases with increasing simultaneously the dielectric constant and the hydrogen ion concentration of the reaction medium and (b) alcohol formation, which occurs via electron transfer between radical species having different redox potentials, increases with decreasing the hydrogen ion concentration of the medium.Under appropriate reaction conditions, the dimerization process is partially stereoselective.Reaction mechanisms are proposed which account for the ratio of both dimer / alcohol and meso / dl under different experimental conditions.
