[reaction: see text] The titanium catalyst, which was generated in situ from titanocene dichloride and 2 equiv of butyllithium, was found to catalyze hydrosilation of a variety of alkynes with excellent regio- and syn-selectivity.
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Quaternary Carbon Synthesis by Titanocene Catalyzed Radical Allyl Transfer on Epoxides.
Org Lett
November 2023
Kekulé-Institute for Organic Chemistry and Biochemistry, University of Bonn, D-53121 Bonn, Germany.
A versatile titanocene-catalyzed radical allyl transfer reaction on epoxides is reported. Epoxide opening occurs regioselectively at the more hindered side, and variously substituted allyl sulfone may be coupled to this position in an efficient manner, enabling a rapid access to quaternary carbon centers with useful functionalities for further elaboration. Furthermore, the procedure can be expanded to stereoselective variants.
View Article and Find Full Text PDFTitanocene-Catalyzed Reductive Domino Epoxide Ring Opening/Defluorinative Cross-Coupling Reaction.
Org Lett
May 2020
Hefei National Laboratory for Physical Science at the Microscale and Department of Chemistry, University of Science and Technology of China, Hefei, Anhui 230026, P. R. China.
Herein, we report a method for efficient synthesis of -difluorobishomoallylic alcohols starting from trifluoromethyl-substituted alkenes and epoxides via a titanocene-catalyzed reductive domino reaction, which consists of a Ti(III)-mediated radical-type ring opening and the following allylic defluorinative cross-coupling reaction via sequential radical addition and β-F elimination. Notably, complete regioselectivity and high tolerance of functionalities can be achieved in this reaction. Furthermore, diverse 6-fluoro-3,4-dihydro-2-pyrans have been prepared through derivatization of the cross-coupling products in one single step.
View Article and Find Full Text PDFMerging Regiodivergent Catalysis with Atom-Economical Radical Arylation.
Angew Chem Int Ed Engl
October 2019
Kekulé-Institut für Organische Chemie und Biochemie, Universität Bonn, Gerhard Domagk-Straße 1, 53121, Bonn, Germany.
A titanocene-catalyzed regiodivergent radical arylation is described that allows access to either enantiomerically pure tetrahydroquinolines or indolines from a common starting material. The regioselectivity of epoxide opening that results in the high selectivity of heterocycle formation is controlled by two factors, the absolute configuration of the enantiopure ligands of the (C H R) TiX catalyst and the inorganic ligand X (X=Cl, OTs). The overall reaction is atom-economical and constitutes a radical Friedel-Crafts alkylation.
View Article and Find Full Text PDFAnti-Markovnikov alcohols via epoxide hydrogenation through cooperative catalysis.
Science
May 2019
Department of Chemistry, Columbia University, 3000 Broadway, New York, NY 10027, USA.
The opening of epoxides typically requires electrophilic activation, and subsequent nucleophilic (S2) attack on the less substituted carbon leads to alcohols with Markovnikov regioselectivity. We describe a cooperative catalysis approach to anti-Markovnikov alcohols by combining titanocene-catalyzed epoxide opening with chromium-catalyzed hydrogen activation and radical reduction. The titanocene enforces the anti-Markovnikov regioselectivity by forming the more highly substituted radical.
View Article and Find Full Text PDFTitanocene-catalyzed regioselective alkylation of styrenes with grignard reagents using beta-bromoethyl ethers, thioethers, or amines.
Chem Asian J
September 2008
Science and Technology Centre for Atoms, Molecules and Ions Control, Graduate School of Engineering, Osaka University, Yamadaoka 2-1, Suita, Osaka 565-0871, Japan.
Regioselective double alkylation of styrenes with alkyl Grignard reagents and alkyl bromides having a heteroatom functional group at the beta-position has been achieved by the use of a titanocene catalyst in THF. When ether was used instead of THF as a solvent, monoalkylation by substitution of a vinylic hydrogen atom with an alkyl group proceeded under similar conditions. These reactions involve the addition of alkyl radicals to styrenes to form benzylic radical intermediates.
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