Reactivity of Methyl Mandelate−Ti(IV)-enediolate: Oxidative Homocoupling versus Aldol and Direct Mannich-Type Syn-Diastereoselective Condensation
摘要:
Methyl mandelate undergoes quantitative oxidative homo-coupling 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 Mannich-type syn-diastereo-selective reaction is observed in the presence of both ArCHO and PhNH2. The subsequent reactions of the title intermediate do not depend on how it is generated.
Key Role of Ti(IV) in the Selective Radical−Radical Cross-Coupling Mediated by the Ingold-Fischer Effect
作者:Raffaele Spaccini、Nadia Pastori、Angelo Clerici、Carlo Punta、Ombretta Porta
DOI:10.1021/ja807613q
日期:2008.12.31
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 alpha,beta-dihydroxy ketones by enhancing the captodative
Efficient diastereoselective synthesis of α,β-Dihydroxyesters from methyl phenylglyoxylate and aldehydes mediated by Titanium Trichloride/Pyridine System
作者:Angelo Clerici、Laura Clerici、Luciana Malpezzi、Ombretta Porta
DOI:10.1016/0040-4020(95)00872-6
日期:1995.11
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