This review article was ranked No.
Cation-triggered switchable asymmetric catalysis with chiral Aza-CrownPhos.
This review is a hot paper 0. Celebrating the 80th Birthday of Professor Ei-ichi Negishi! This article was ranked No. Highlighted in C hinese Journal of Organic Chemistry , , 33 12 , This paper was one of the most read articles in Nov.
Featured on organic-chemistry. Corrigendum : Tetrahedron Lett.
- Catalysis. Leibniz-Institut für Katalyse. Forschung über Katalysatoren: Publications.
- Reward Yourself!
- Asymmetric Catalysis from a Chinese Perspective (Topics in Organometallic Chemistry, Volume 36).
- What is Kobo Super Points?.
This paper was one of the most read articles in Mar. This paper was selected as a hot paper. This paper was one of the most read articles in July This paper was one of the most read articles in August. Some mechanistic insights were also presented. Keywords: Asymmetric reactions, catalysis, chiral titanium complexes Introduction Asymmetry is one of the general features of nature.
- Dynamics And Bifurcation Of Patterns In Dissipative Systems.
- Dipartimenti | Consiglio Nazionale delle Ricerche.
- Advances in Dynamic Game Theory: Numerical Methods, Algorithms, and Applications to Ecology and Economics;
- Martial Arts of the World: An Encyclopedia?
- Structure/Ornament and the Modern Figuration of Architecture.
- Posted on 13-09-12222.
- Asymmetric reactions catalyzed by chiral titanium complexes.
Chiral molecules play essential roles in physiological process of life, as well as in high-technical fields, owing to its unique physical and biochemical properties. In the last decades, brilliant achievements have been made to provide optically pure or enantiomer-enriched chemicals by employ-ing specific ligand-metal complex, as a remarkable consequence of the coordination chemistry of transition metals,1, 2a to catalyze or promote some asymmetric reactions.
Herein, we reviewed our recent progress in asymmetric reactions catalyzed by chiral titanium complexes. Transition metal titanium shows a special electronic configuration in the atomic orbit and coordination behavior. Titanium chemistry has been highly developed,2a-b and titanium has also been extensively applied to asymmetric synthesis as Lewis acid.
Join Kobo & start eReading today
Silylcyanation of aldehydes and related ligands. Table 1. Table 2. In addition, the basicity of counter ions CI showed more effect on the. Based on these experimental results, a working transition state of the catalyst was proposed as Figure 1.
Chiral Ferrocenes in Asymmetric Catalysis
The working transition state for the silylcyanation of aldehydes. In conclusion, an effective catalyst for asymmetric silylcyanation of aldehydes has been developed. The further modification of the ligand structure should be aimed to extend this catalyst system to asymmetric trimethylsilylcyanation of ketones and imines.
Oxazolines involved in the asymmetric oxidation of sulfides. The direct asymmetric oxidation of sulfides approach has received tremendous attention in the area of organic synthesis. Excellent enantioselectivity has been reported by Kagan and other groups in the past 20 years, 12 but the ligands were extremely limited within diols and Schiff bases. Oxazoline, another class of important chiral auxiliaries, has been successfully employed in. Bolm tried out the oxazoline-vanadium IV complex on the oxidation of prochiral sulfides, but failed with racemic sulfoxides. Table 3.
In brief, we have first probed and developed a novel effective oxazoline-titanium IV catalyst system for the asymmetric oxidation of sulfides. Further study should be focused on the fine tuning of the ligand structure for both selectivity and substrate generality.
Additionally, the products were readily transformed into biologically active spirooxazolines. Importantly, using a model of acute neuroinflammation, several of the spirooxazolines were found to significantly reduce LPS-induced fever. Although isothiocyanates have previously been applied in the synthesis of cyclic aldol products [ 10 — 14 ], this represents the first example in the construction of spirocyclic oxindoles using 3-isothiocyanato oxindoles through direct aldol reaction.
It is worthy to note that there is no change in the stereoselectivities during the various transformations.
Cation-triggered switchable asymmetric catalysis with chiral Aza-CrownPhos. - PDF Download Free
Importantly, in most instances, high reactivity was observed and the reaction could be completed even within 1. The potential application of this method was demonstrated by a large- scale experiment and by the further transformation of one product. In addition, the products of this reaction can be modified to allow easy access to differently functionalized spirooxindoles. Notably, the additive p -CNC 6 H 4 CO 2 H in the reaction had an important influence on the reactivity and asymmetric induction, which attribute to the hydrogen and the guanidine moiety both played crucial roles in the process.
And preliminary biological studies revealed that several of the methylthioimidazoline derivatives showed extremely promising antipyretic activity. Feng proposed that the weakly acidic additive p -CNC 6 H 4 CO 2 H could protonate one of the guanidine moieties leading to a guanidinium salt, which activates the N -Ts-imine via hydrogen bond to the nitrogen of the N -Ts-imine.
On the other hand, Wang proposed that the rosin-derived tertiary amine—thiourea 8g would act in a bifunctional fashion. Concurrently, N -Ts-imine 30 was located and activated by two hydrogen atoms of the thiourea moiety through hydrogen-bond interaction. Afterwards, the nucleophile would preferentially attack at the N -Ts-imine 30 from the Re -face, since the Si -face of the N -Ts-imine 30 was restricted by the quinine moiety of the catalyst.
Importantly, N -PMP aldimine, N -diphenylphosphinoyl aldimine, and N -Boc isatinimine were also good substrates for reacting with 3-isothiocyanato oxindoles 2. A possible model for explaining the stereochemistry of the domino Mannich—cyclization reaction was proposed. Dimethylpyrazole was selected as the directing group, because there would have interaction between the pyrazole group and the thiourea moiety of the catalyst.
Additionally, the acetyl protecting group played a crucial role in the enantioselectivity.
Undoubtedly, this methodology provides a convenient and highly efficient approach for the construction of spiropyrazolone skeletons with high enantioselectivities. The following examples illustrate the progress in this area.