Catalytic asymmetric processes

Wills, Martin

doi:10.1039/a706653h

Cited by 25 publications

(11 citation statements)

References 191 publications

(205 reference statements)

Supporting

Mentioning

Contrasting

Unclassified

Order By: Relevance

“…Chiral Lewis acid catalysis provides the ability to control the enantioselectivity of the simultaneous formation of several stereogenic centers at lower temperatures [1,27,[66][67][68][69]. This reaction is particularly valuable for the formation of six-membered rings and often involves the reaction of an enal or enone with a diene.…”

Section: Cycloadditions Via Diels-alder Reactionsmentioning

confidence: 99%

Lewis Acid Catalysis by Ruthenium Complexes

Faller¹,

Parr²

2006

COC

View full text Add to dashboard Cite

Recent progress in the Lewis acid catalysis of organic reactions by ruthenium complexes. The review focuses on reactions in which coordinatively unsaturated ruthenium species function as conventional Lewis acids, rather than those involving oxidation or reduction, such as in hydrogenations. Particular emphasis is placed on the development of asymmetric catalysts. INTRODUCTIONLewis acid catalysis continues to be of major utility in organic synthesis [1]. Recent interest in asymmetric catalysis [2,3], particularly for the formation of carbon-carbon bonds, has spurred continuing developments in chiral Lewis acid catalysts [4][5][6]. Classically, Lewis acid catalysts would have involved: main group elements, such as boron or aluminum; tin or zinc; early transition metals, such as titanium; or some lanthanides. Koga developed one of the earliest successful main group catalysts [7]. Yamamoto has been a major contributor to the development of chiral main group Lewis acid catalysts [1,8]. Organometallic Lewis acids of late transition metals have been extensively studied by Beck [9], but the potential for stoichiometric asymmetric reactions on coordinated ligands was largely developed by others, particularly with rhenium [10,11] and molybdenum reagents [12]. These studies of stoichiometric reactions provided valuable information regarding mechanistic aspects and control of nucleophilic attack on coordinated substrates. The lack of sensitivity to decomposition from moisture is a particular advantage of the late transition metal Lewis acids and the potential for straightforward elaboration of the chirality at the metal center via ligand variation has allowed the development of effective asymmetric catalysts based on these metals. Lewis-acid catalysts based on ruthenium have been particularly effective and recent developments on this area will be covered here. Since the mechanisms of a large number of reactions catalyzed by ruthenium complexes involve loss of a ligand to provide a site for coordination of a substrate, a large fraction of the reactions could be viewed as involving Lewis acids. Thus this overview could cover much of the material in a recent monograph [13] which included 383 pages dedicated to ruthenium in organic synthesis. Nevertheless, we will primarily focus on reactions that have been traditionally viewed as catalyzed by Lewis acids and only provide a brief discussion of reactions in which one would expect the oxidation state of the ruthenium to change during the catalytic cycle. Another specific review and more general reviews are also recommended [13][14][15][16].

show abstract

Section: Cycloadditions Via Diels-alder Reactionsmentioning

confidence: 99%

Lewis Acid Catalysis by Ruthenium Complexes

Faller¹,

Parr²

2006

COC

View full text Add to dashboard Cite

show abstract

“…As a result, there are meanwhile powerful asymmetric catalytic variants for many basic reactions. [2] However, until recently this did not include the important class of aminoalkylation reactions, [3] if one leaves aside aminoalkylations of Grignard, organolithium, or organozinc compounds catalyzed by chiral ligands (Lewis bases). [4] Attempts to activate and to modify other nucleophiles such as ester enolates [5a,b] or HCN [5c] chirally with ligands or Lewis bases (diether, [5a,b] dipeptide [5c] ) and to aminoalkylate them enantioselectively were only partly successful.…”

mentioning

confidence: 99%

Asymmetric Catalytic Aminoalkylations: New Powerful Methods for the Enantioselective Synthesis of Amino Acid Derivatives, Mannich Bases, and Homoallylic Amines

Arend¹,

Wang²

2003

Organic Synthesis Highlights V

View full text Add to dashboard Cite

The economic importance of enantiomerically pure compounds has grown considerably during the last years and will increase even further. [1] Therefore, the development of efficient asymmetric syntheses with chiral catalysts is a main focus of modern industrial and basic research. As a result, there are meanwhile powerful asymmetric catalytic variants for many basic reactions. [2] However, until recently this did not include the important class of aminoalkylation reactions, [3] if one leaves aside aminoalkylations of Grignard, organolithium, or organozinc compounds catalyzed by chiral ligands (Lewis bases). [4] Attempts to activate and to modify other nucleophiles such as ester enolates [5a,b] or HCN [5c] chirally with ligands or Lewis bases (diether, [5a,b] dipeptide [5c] ) and to aminoalkylate them enantioselectively were only partly successful. These methods either require a stoichiometric amount of the chiral ligand or provide good ee values solely in special cases. However, recently it has been shown impressively that the potential of this methodology is definitely not exhausted yet. Thus, a relatively efficient and broadly applicable asymmetric variant of the Strecker synthesis could be developed by optimization of a Lewis base catalyst using combinatorial methods (Scheme 1). [5d] Scheme 1. Base-catalyzed enantioselective variant of the Strecker synthesis (R alkyl, aryl). [5d] More recent publications demonstrate the extraordinary potential of an alternative synthetic strategy: the use of chiral Lewis acid catalysts for the activation and chiral modification of Mannich reagents (generally imino compounds). In this way, not only HCN or its synthetic equivalents [6] but also numerous other nucleophiles could be aminoalkylated asymmetrically (e.g. trimethylsilyl enol ethers derived from esters [7±9a] or ketones, [9] alkenes, [10] allyltributylstannane, [11 a] allyltrimethylsilanes, [9a, 11b] and ketones [12] ). Thus, efficient routes for the enantioselective synthesis of a variety of valuable synthetic building blocks were created (e.g. a-aminonitriles, [6] a-or b-amino acid derivatives, [7±10] homoallylic amines, [9a, 10±11] or b-amino ketones [9,12] ).Most of the hitherto published methods employ imino compounds that can act as bidentate ligands and form chelate complexes with the chiral Lewis acid catalysts. On the other hand, simple Mannich reagents usually furnish significantly lower ee values. [9c, 12] One can easily explain this by the restriction of the configurational diversity in the chelate complexes, [9d] favoring a stereochemically uniform course of the reaction.Thus, N-(2-hydroxyphenyl)imines 1 (R alkyl, aryl) together with zirconium catalysts (binaphthol derivatives) generated in situ were used successfully for the asymmetric synthesis of a-aminonitriles [6a] and simple b-amino acid derivatives [7a,c] or for the diastereo-and enantioselective preparation of a-hydroxy-b-amino acid derivatives. [7b] The advantages of the methodology include good yields and stereoselectivi...

show abstract

“…

The economic importance of enantiomerically pure compounds has grown considerably during the last years and will increase even further. [2] However, until recently this did not include the important class of aminoalkylation reactions, [3] if one leaves aside aminoalkylations of Grignard, organolithium, or organozinc compounds catalyzed by chiral ligands (Lewis bases). As a result, there are meanwhile powerful asymmetric catalytic variants for many basic reactions.

…”

mentioning

confidence: 99%

“…Asymmetric catalytic aminoalkylation as the key step in the diastereo-and enantioselective synthesis of (2R,3S)-3-phenylisoserine hydrochloride (2) Asymmetric catalytic aminoalkylation as the key step in the diastereo-and enantioselective synthesis of (2R,3S)-3-phenylisoserine hydrochloride (2)…”

mentioning

confidence: 99%