Journal ArticleDOI
Enantioselective palladium-catalyzed addition of 1,3-dicarbonyl compounds to an allene derivative.
TLDR
Enhancing atom economy of the metal-catalyzed asymmetric allylic alkylation shifts from the usual nucleophilic displacement of a leaving group to an addition of a pronucleophile to a double bond with excellent regioselectivity and enantiomeric excess under optimized conditions.Abstract:
Enhancing atom economy of the metal-catalyzed asymmetric allylic alkylation (AAA) shifts from the usual nucleophilic displacement of a leaving group to an addition of a pronucleophile to a double bond. Using 1-alkoxyallenes as proelectrophiles, the palladium-catalyzed AAA proceeds with 1,3-dicarbonyl compounds as pronucleophiles with excellent regioselectivity and enantiomeric excess under optimized conditions. The pH of the medium proved crucial for reactivity/ selectivity. By using the more acidic Meldrum's acids, the reactions required a co-catalytic amount of Bronsted acid. such as trifluoroacetic acid. Single regioisomeric products of 82-99% ee were obtained. On the other hand, the less acidic 1,3-diketones failed to react under such conditions. The fact that a less acidic acid like benzoic acid sufficed, suggested the need for general base catalysis as well. Thus, a mixture of triethylamine and benzoic acid proved optimal (ee's 93-99). Employment of the (/?,/?)-phenyl Trost ligand gave a product with S configuration. A model to rationalize the results has been developed.read more
Citations
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Metal-catalyzed enantioselective allylation in asymmetric synthesis.
TL;DR: Metal-catalyzed enantioselective allylation, which involves the substitution of allylic metal intermediates with a diverse range of different nucleophiles or S(N)2'-type allylic substitution, leads to the formation of C-H, -C, -O, -N, -S, and other bonds with very high levels of asymmetric induction.
Journal ArticleDOI
Metallkatalysierte enantioselektive Allylierungen in der asymmetrischen Synthese
TL;DR: In this article, metallkatalysierte enantioselektive Allylierungen, die unter Substitution von Allylmetall-Zwischenstufen mit zahlreichen Nucleophilen oder als allylische SN2′-Substitution verlaufen, werden in Gegenwart ausgewahlter Kombinationen aus Metallen and chiralen Liganden C-H-, C-C-, C-, C O-, C N-, C S
Journal ArticleDOI
Sugars, Alkaloids, and Heteroaromatics: Exploring Heterocyclic Chemistry with Alkoxyallenes†
TL;DR: Alkoxyallenes have proven themselves to be powerful C(3) building blocks toward complex molecular targets, revealing novel pathways to a variety of desirable highly functionalized heterocycles.
Journal ArticleDOI
Additive Effects on Asymmetric Catalysis
TL;DR: This review highlights a number of additives that can be used to make asymmetric reactions perfect, such as reduced reaction time, improved yield, or/and increased selectivity.
Journal ArticleDOI
Branching Out: Rhodium-Catalyzed Allylation with Alkynes and Allenes
Philipp Koschker,Bernhard Breit +1 more
TL;DR: This new methodology offers an attractive alternative to other established methods for allylic functionalization such as allylic substitution or allylic oxidation and grants access to an important structural class valued in modern organic chemistry for both its versatility for further functionalization and the potential for asymmetric synthesis with the construction of a new stereogenic center.
References
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Journal ArticleDOI
The atom economy--a search for synthetic efficiency
TL;DR: Transition metal-catalyzed methods that are both selective and economical for formation of cyclic structures, of great interest for biological purposes, represent an important starting point for this long-term goal.
Journal ArticleDOI
Asymmetric Transition Metal-Catalyzed Allylic Alkylations.
TL;DR: The focus of this review is on the area of enantioselective transition metal-catalyzed allylic alkylations which may involve C-C as well as C-X (X ) H or heteroatom) bond formation.
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Equilibrium Acidities in Dimethyl Sulfoxide Solution
TL;DR: The first acidity scale to be established in a pure solvent other than water was the result of the pioneering work of Conant, Wheland, and McEwen in ether or ben~ene.
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Asymmetric transition-metal-catalyzed allylic alkylations: applications in total synthesis.
TL;DR: Alkylations with Phenols, Nitrogen Nucleophiles in AAA Total Synthesis, and Considerations for Enantioselective Allylic Alkylation are presented.
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Atom Economy—A Challenge for Organic Synthesis: Homogeneous Catalysis Leads the Way
TL;DR: The ability of transition metal complexes to preorganize π-electron systems serves as the basis both of simple additions usually accompanied by subsequent hydrogen shifts and of cycloadditions as mentioned in this paper.