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ACDC Catalysts

We then thought to carry out conjugate reduction of a,P-unsaturated ketones. However, neither these ACDC-catalysts, nor the commonly... [Pg.32]

S.C. PanandB. List s paper spans the whole field of current organocat-alysts discussing Lewis and Brpnsted basic and acidic catalysts. Starting from the development of proline-mediated enamine catalysis— the Hajos-Parrish-Eder-Sauer-Wiechert reaction is an intramolecular transformation involving enamine catalysis—into an intermolecular process with various electrophilic reaction partners as a means to access cY-functionalized aldehydes, they discuss a straightforward classification of organocatalysts and expands on Brpnsted acid-mediated transformations, and describe the development of asymmetric counteranion-directed catalysis (ACDC). [Pg.351]

In 2008, List s group developed an epoxidation using asymmetric counteranion-directed catalysis (ACDC) [177]. In this work, the epoxidation of 1,2-disubstituted enals (33) and (3,(3-disubstituted, a, 3-unsaturated aldehydes (115) was explored. Instead of using a chiral amine (e.g. Jprgensen-Hayashi s catalyst), an achiral amine and a chiral counteranion (a phosphoric acid derived from BINOL), were employed. [Pg.455]

Besides the utilization of chiral secondary amines to achieve a LUMO-lowering activation as well as face discrimination, the use of achiral secondary amines in combination with a chiral counterion also proved to be highly promising for such transformations. This strategy resembles the use of achiral metal catalysts in combination with a chiral ligand to achieve a stereoselective transformation (206-208). It is due to Benjamin List that the elegant concept of asymmetric counteranion-directed catalysis (ACDC) has found widespread applications in organocatalysis at the present time (209-212). [Pg.56]

In the case of enals, the most common catalysts are secondary chiral amines, which can be divided into two large groups (i) amines substituted with a bulky group and (ii) amines with hydrogen-bond-directing groups. Another possible type of catalyst for this activation mode arises from ACDC (asymmetric counterion direct catalysis) developed by List. In these catalysts either a chiral or non-chiral amine forms a chiral ionic pair with a chiral phosphoric acid. A different possibility is the use of a primary chiral amine and a strong acid. These latter methods have... [Pg.979]

Although a,P-unsaturated aldehydes have been used extensively in F-C alkylations since 2001, the first report on a,P-unsaturated enones as electrophiles appeared only in 2006 [51]. In this publication, indole reacts with 5-methyl-3-hexen-2-one to afford the desired product in moderate yield (52%) and low enantioselectivity (28% ee). One year later, two independent groups showed that the utilization of primary amines 9 and 10 derived from natural cinchona alkaloids facilitates the iminium formation with unsaturated enones instead of hindered secondary amine catalysts [15,16]. It should be emphasized that in both cases the use of an acidic co-catalyst is necessary to achieve the transformations. Nevertheless, only the second one, with catalyst 10, profited from an asymmetric counterion-directed organocatalytic system (ACDC) [52] (Scheme 35.3). [Pg.1047]

Amino catalysts are one of the most dominant organocatalysts in the activation and transformation of aldehydes or ketones through enamine or iminium intermediates. Initially, the presence of an acid co-catalyst is crucial for the catalytic activation. Later it was reaUzed that the introduction of a chiral counteranion to the catalytic system enables the reactions proceeding through cationic intermediates to be conducted in a highly enantioselective manner, and thus stereochemical control could be effectively induced by the chiral counteranion. This strategy has been defined as asymmetric counterion-directed catalysis (ACDC) [25]. [Pg.1343]

While asymmetric counteranion-directed catalysis (ACDC) has been estab-hshed as a powerful strategy in iminium catalysis, enamine-based asymmetric counteranion-directed catalysis has not yet been developed. Recently, Lu et al. [32] demonstrated that the combination of a cinchona alkaloid-derived primary amine and chiral camphorsuhnnic acid (CSA) results in an effective ion-pair catalyst for the directed asymmetric amination of a-branched aldehydes through enamine activation (Scheme 43.21). [Pg.1346]

Asymmetric hydride reduction using Hantzsch ester has recently been extensively explored in organocatalysis using iminium-based catalysts or Brpnsted acid catalysts [72a-c], As an advance to their asymmetric conterion-directed catalysis (ACDC), List and coworkers found that the combination of simple primary amino acids such as L-valine with a chiral phosphoric acid led to an effective primary aminocatalyst for asymmetric transfer hydrogenation of a,P-unsaturated ketones (Scheme 5.43) [72d]. The catalysis could be applied to a range of substrates with good yields and excellent enantioselectivity. [Pg.172]


See other pages where ACDC Catalysts is mentioned: [Pg.982]    [Pg.982]    [Pg.982]    [Pg.982]    [Pg.29]    [Pg.66]    [Pg.6]    [Pg.49]   


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