Reagent‐Controlled Stereoselectivity in Titanocene‐Catalyzed Epoxide Openings: Reductions and Intermolecular Additions to <i>α</i>,<i>β</i>‐Unsaturated Carbonyl Compounds

Gansäuer, Andreas; Bluhm, Harald; Rinker, Björn; Narayan, Sanjay; Schick, M.; Lauterbach, Thorsten; Pierobon, Marianna

doi:10.1002/chem.200390056

Cited by 112 publications

(40 citation statements)

References 78 publications

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“…[12] In both cases investigated, none of the products arising from radical reduction prior to C À C bond formation could be isolated. This is not aproblem under our conditions,a ss ummarized in Scheme 4.…”

Section: Methodsmentioning

confidence: 94%

Amide‐Substituted Titanocenes in Hydrogen‐Atom Transfer Catalysis

et al. 2015

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Two new catalytic systems for hydrogen-atom transfer (HAT) catalysis involving the N-H bonds of titanocene(III) complexes with pendant amide ligands are reported. In a monometallic system, a bifunctional catalyst for radical generation and reduction through HAT catalysis depending on the coordination of the amide ligand is employed. The pendant amide ligand is used to activate Crabtree's catalyst to yield an efficient bimetallic system for radical generation and HAT catalysis.

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Section: Methodsmentioning

confidence: 94%

Amide‐Substituted Titanocenes in Hydrogen‐Atom Transfer Catalysis

et al. 2015

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“…TS‐A is destabilized through the interaction of the incoming 1,4‐cylclohexadien with the axial OTBS group, while in TS‐B the bulky titanocene moiety interacts with TBS. However, observations by Giese and Gansäuer on similar substrates confirm that the repulsion between the CH 2 O[TiCp 2 Cl] group and a nearby axial bulky substituent guides the radical trap to the opposite face . In the case of the fluoro‐carba‐glucosamine precursor 3 , this would lead to the observed equatorial arrangement of the hydroxy methylene group through the axial attack of 1,4‐cyclohexadiene.…”

Section: Resultsmentioning

confidence: 95%

Fluoro‐Carba‐Sugars are Glycomimetic Activators of the glmS Ribozyme

Matzner

Schüller

Seitz

et al. 2017

Chemistry A European J

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The glmS ribozyme is a bacterial gene-regulating riboswitch that controls cell wall synthesis, depending on glucosamine-6-phosphate as a cofactor. Due to the presence of this ribozyme in several human pathogen bacteria (e.g., MRSA, VRSA), the glmS ribozyme represents an attractive target for the development of artificial cofactors. The substitution of the ring oxygen in carbohydrates by functionalized methylene groups leads to a new generation of glycomimetics that exploits distinct interaction possibilities with their target structure in biological systems. Herein, we describe the synthesis of mono-fluoro-modified carba variants of α-d-glucosamine and β-l-idosamine. (5aR)-Fluoro-carba-α-d-glucosamine-6-phosphate is a synthetic mimic of the natural ligand of the glmS ribozyme and is capable of effectively addressing its unique self-cleavage mechanism. However, in contrast to what was expected, the activity is significantly decreased compared to its non-fluorinated analog. By combining self-cleavage assays with the Bacillus subtilis and Staphylococcus aureus glmS ribozyme and molecular docking studies, we provide a structure-activity relationship for fluorinated carba-sugars.

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“…To this end we chose the commercial Brintzinger complex dichloroA C H T U N G T R E N N U N G (R,R)-ethylenebis(4,5,6,7-tetrahydro-1-indenyl)titanium(IV) (52) and Kagans complex 53 prepared in our laboratory. [38] Allylation of 3,4,5-trimethoxybenzaldehyde (19) catalyzed by 52 gave a 50 % yield of (S)-(À)-25, [39] with a 33 % enantiomeric excess (ee) (Scheme 5). [40] Moreover, the allylation of 2 catalyzed by 53 afforded an 80 % yield of (S)-(À)-10, [41] with a 20 % ee.…”

Section: Resultsmentioning

confidence: 99%

Ti‐Catalyzed Barbier‐Type Allylations and Related Reactions

Estévez

Justicia

Bazdi

et al. 2009

Chemistry A European J

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Titanocene(III) complexes, easily generated in situ from commercial Ti(IV) precursors, catalyze Barbier-type allylations, intramolecular crotylations (cyclizations), and prenylations of a wide range of aldehydes and ketones. The reaction displays surprising and unprecedented mechanistic subtleties. In cyclizations a fast and irreversible addition of an allyl radical to a Ti(III)-coordinated carbonyl group seems to occur. Intermolecular additions to conjugated aldehydes proceed through a coupling of a Ti(IV)-bound ketyl radical with an allyl radical. Reactions of ketones with allylic halides take place by the classical addition of an allylic organometallic reagent. The radical coupling processes enable transformations such as the highly regioselective alpha-prenylation that are otherwise difficult to achieve. The mild reaction conditions and the possibility to employ titanocene complexes in only catalytic quantities are highly attractive features of our protocol. These unusual properties have been taken advantage of for the straightforward synthesis of the natural products rosiridol, shikalkin, and 12-hydroxysqualene.

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Reagent‐Controlled Stereoselectivity in Titanocene‐Catalyzed Epoxide Openings: Reductions and Intermolecular Additions to α,β‐Unsaturated Carbonyl Compounds

Cited by 112 publications

References 78 publications

Amide‐Substituted Titanocenes in Hydrogen‐Atom Transfer Catalysis

Amide‐Substituted Titanocenes in Hydrogen‐Atom Transfer Catalysis

Fluoro‐Carba‐Sugars are Glycomimetic Activators of the glmS Ribozyme

Ti‐Catalyzed Barbier‐Type Allylations and Related Reactions

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