Structurally Diverse Second‐Generation [2.2]Paracyclophane Ketimines with Planar and Central Chirality: Syntheses, Structural Determination, and Evaluation for Asymmetric Catalysis

Lauterwasser, Frank; Nieger, Martin; Mansikkamäki, Heidi; Nättinen, Kalle; Bräse, Stefan

doi:10.1002/chem.200500146

Cited by 29 publications

(17 citation statements)

References 72 publications

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“…[14 -17] In particular, the asymmetric 1,2-addition reaction of zinc reagents [18] such as alkyl, [19 -21] alkenyl, [22] aryl [23] and alkynyl [24] zinc reagents with aldehydes or imines, [19,20,23] can be efficiently controlled by the application of hydroxy[2.2]paracyclophane ketimine ligands.…”

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confidence: 99%

“…[10 -13] Within the last few years, various new paracyclophane ligands have been used for asymmetric catalysis. [14 -17] In particular, the asymmetric 1,2-addition reaction of zinc reagents [18] such as alkyl, [19 -21] alkenyl, [22] aryl [23] and alkynyl [24] zinc reagents with aldehydes or imines, [19,20,23] can be efficiently controlled by the application of hydroxy[2.2]paracyclophane ketimine ligands.[17]We recently reported the synthesis of the [2.2]paracyclophane-based ketimine ligands (R P ,S)-2, (S P ,S)-2, (R P ,S)-3, and (S P ,S)-3 and their application in asymmetric catalysis such as the addition of zinc reagents to aldehydes. [19] During these studies, we observed not only that these ligands are highly active, [21,25] but also that they display mismatched and matched cases.…”

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Planar‐ and Central‐Chiral N,O‐[2.2]Paracyclophane Ligands: Non‐Linear‐Like Effects and Activity

Lauterwasser¹,

Vanderheiden²,

Bräse³

2006

Adv Synth Catal

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The non-linear-like effect (NLLE), activity, temperature dependence, and kinetics of hydroxy-[2.2]paracyclophane ketimine ligands have been investigated with the 1,2-addition reaction of diethylzinc to cyclohexanecarbaldehyde. A linear correlation between the enantiomeric excess of AHPC ketimine ligands bearing a phenylethyl side group and the product was observed with 0.5 mol % of catalyst loading. On increasing the catalyst loading to 4 mol %, a precipitate of the inactive heterochiral species was formed and resulted in a positive nonlinear-like effect. The enantiomeric ratio was found to have linear temperature dependence.Keywords: asymmetric catalysis; catalytic activity; non-linear-like effect; paracyclophanes Asymmetric catalysis often displays a relationship between selectivity and reactivity. Intricate molecular mechanisms with a number of rate constants often lead to complex rate laws. The latter have not been elucidated in most cases although attempts have been made to unravel them.[1] Features such as non-linear effects, [2] autocatalysis, [3] reservoir effects, chiral poisoning, [4] and asymmetric activation [5] have been discovered in asymmetric catalytic reactions.[6] In particular, the strong non-linear effect associated with Noyoris DAIB ligand in the addition of diethylzinc to benzaldehyde has been thoroughly investigated.[7a]Since the initial reports of Reich and Cram, [8] the field of [2.2]paracyclophane chemistry has grown considerably.[9] The chemical behavior of [2.2]paracyclophanes is currently well understood allowing predictable modification of this relatively stable class of molecules. [10 -13] Within the last few years, various new paracyclophane ligands have been used for asymmetric catalysis. [14 -17] In particular, the asymmetric 1,2-addition reaction of zinc reagents [18] such as alkyl, [19 -21] alkenyl, [22] aryl [23] and alkynyl [24] zinc reagents with aldehydes or imines, [19,20,23] can be efficiently controlled by the application of hydroxy[2.2]paracyclophane ketimine ligands.[17]We recently reported the synthesis of the [2.2]paracyclophane-based ketimine ligands (R P ,S)-2, (S P ,S)-2, (R P ,S)-3, and (S P ,S)-3 and their application in asymmetric catalysis such as the addition of zinc reagents to aldehydes. [19] During these studies, we observed not only that these ligands are highly active, [21,25] but also that they display mismatched and matched cases. [19,22] In general, the [2.2]paracyclophane backbone determines the configuration of the product. However, it was possible to finetune the ligand system by adjusting the side groups.The successful applications of these [2.2]paracyclophane-based ligands led to further investigations of this system. In this manuscript, we disclose our findings which lead to a deeper understanding of this ligand class. We present studies of the non-linear-like effect (NLLE) [26] with the enantiomeric pairs 1 and 3, respectively. In addition, we investigated the activity of the diastereomers (R P ,S)-2 and (S P ,S)-2 and the diaste...

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Planar‐ and Central‐Chiral N,O‐[2.2]Paracyclophane Ligands: Non‐Linear‐Like Effects and Activity

Lauterwasser¹,

Vanderheiden²,

Bräse³

2006

Adv Synth Catal

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“…Ligands were synthesized according to literature procedures. [23] Enantiomeric excesses were determined by GC on chiral stationary phase (Varian with CPChirasil-Dex CB, 25 m 0.25 mm, 0.25 mm), or by HPLC (Agilent with Diacel Chiracel OD, 250 4.00 mm, 10 mm). C NMR spectra were recorded on Bruker AC 250 (250 MHz/62.5 MHz), Bruker AM 400 (400 MHz/ 100 MHz) and Bruker DRX 500 (500 MHz/125 MHz) spectrometers using CDCl 3 as the solvent and shift reference (7.26 ppm/77.00 ppm).…”

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confidence: 99%

“…[25] Here we present an extension on the highly selective alkenyl transfer onto aliphatic and aromatic aldehydes using the second generation of these N,O-[2.2]paracyclophane-based ligands 1 and 2. Our goal was to investigate whether our ligands which showed the best activity and selectivity in the diethylzinc addition [23,24] also catalyze the alkenylzinc addition and to investigate which substrates are tolerated. There-…”

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confidence: 99%

“…We recently reported the synthesis of the N,O-[2.2]paracyclophane-based ligands (R P ,S)-1, (S P ,S)-1, (R P ,S)-2, and (S P ,S)-2 ( Figure 1) and their application in asymmetric catalysis. [23,24] In addition, we carried out non-linear-like effect and activity studies for this class of ligands. [25] Here we present an extension on the highly selective alkenyl transfer onto aliphatic and aromatic aldehydes using the second generation of these N,O-[2.2]paracyclophane-based ligands 1 and 2.…”

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Second‐Generation N,O‐[2.2]Paracyclophane Ketimine Ligands for the Alkenylzinc Addition to Aliphatic and Aromatic Aldehydes: Scope and Limitations

et al. 2006

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Second generation N,O-[2.2]paracyclophane ketimine ligands were investigated for their ability to catalyze the 1,2-addition of alkenylzinc reagents to aliphatic and aromatic aldehydes with special focus on functionalized substrates. For aliphatic aldehydes, which have always been challenging in this field, remarkably high enantiomeric excesses could be determined (50-95 % ee). However, alkenylzinc reagents bearing heteroatoms proved to be demanding substrates for this system. Keywords: alkenylzinc reagents; asymmetric catalysis; chiral allylic alcohols; N,O ligands; paracyclophanes Chiral allylic alcohols are important targets in organic synthesis, especially in natural product synthesis. As intermediates they can be used in further reactions such as allylic substitution, dihydroxylation, ene reaction, cyclopropanation, bromination, or epoxidation. However, the lack of a powerful ligand system impedes the use of the 1,2-addition of alkenylzinc reagents to aldehydes as a key step in natural product synthesis because highly functionalized substrates must be tolerated and high enantiomeric excesses must be achieved.[1] The rare examples in the literature show mostly the use of divinylzinc and substrateinduced diastereoselectivity. [2] In the case of substrate toleration, the catalyzed alkenylzinc addition could be an appropriate method because of the relatively low reactivity of zinc diorganyls towards aldehydes and ketones in comparison to other organometal compounds.[3] However, investigations in this field are few. In contrast, alkyl transfer to aromatic aldehydes is one of the most studied enantioselective catalytic reactions, yet there are only a few examples with high enantiomeric excesses for aliphatic aldehydes.[4] The alkenylzinc transfer is even less investigated; however, interest in this reaction has increased throughout the last years. [5][6][7][8][9][10][11][12] One method elaborated by Oppolzer and Radinov produces mixed alkyl-alkenylzinc species in situ using a transmetalation protocol involving hydroboration of alkynes.[2]paracyclophane-based ligands produce results ranging from good to excellent for this type of reaction, whereas the scope is limited to aromatic aldehydes and fully branched aliphatic aldehydes.[11] Wipf et al. also reported the preparation of alkenylzinc reagents via transmetalation but using zirconium as metal. [9] A comprehensive survey of [2.2]paracyclophanebased ligands can be found in recent reviews.[13] The use of planar-chiral and central-chiral ligands based on paracyclophane systems has emerged en masse since the disclosures by Belokon, Rozenberg et al., [14,15] the Berkessel group, [16] and most notably the Hopf group.[17] Within the last years, various new paracyclophane ligands have been used for asymmetric catalysis. [18][19][20] In particular, the asymmetric 1,2-addition reaction of organozinc compounds such as alkyl-, [21] alkenyl-, [11] and alkynylzinc [22] reagents with aldehydes or imines, [21] respectively, can be efficiently controlled by the use of...

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Catalysis of Organic Processes by Metal Phenolates

Serra¹,

Murtinho²

2012

Patai's Chemistry of Functional Groups

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Transition metal catalysts with phenolates as ligands constitute an extensive class of complexes with application in a great variety of catalytic transformations.Because phenol groups can be sterically and electronically modified by the introduction of substituents with different characteristics, the door is opened to a myriad of catalysts with characteristics of reactivity and selectivity for promoting innumerous transformations of synthetic interest in organic chemistry. Metal phenolates have therefore become essential participants in catalytic organic synthesis, including catalytic asymmetric synthesis. Oxidations of alkenes, sulfides, alcohols and alkanes, additions of trimethylsilylcyanide, diorganozincs and nitroalkanes to CO and CN bonds and Diels–Alder reactions are some examples of the types of reactions that are promoted by these catalysts. This chapter provides an overview of recent advances in the catalysis of organic processes by metal phenolates, with emphasis on the last decade.

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Structurally Diverse Second‐Generation [2.2]Paracyclophane Ketimines with Planar and Central Chirality: Syntheses, Structural Determination, and Evaluation for Asymmetric Catalysis

Cited by 29 publications

References 72 publications

Planar‐ and Central‐Chiral N,O‐[2.2]Paracyclophane Ligands: Non‐Linear‐Like Effects and Activity

Planar‐ and Central‐Chiral N,O‐[2.2]Paracyclophane Ligands: Non‐Linear‐Like Effects and Activity

Second‐Generation N,O‐[2.2]Paracyclophane Ketimine Ligands for the Alkenylzinc Addition to Aliphatic and Aromatic Aldehydes: Scope and Limitations

Catalysis of Organic Processes by Metal Phenolates

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