New Insights in the Search for Chiral Brønsted Bases

Plaquevent, Jean‐Christophe; Perrard, Thierry; Cahard, Dominique

doi:10.1002/1521-3765(20020802)8:15<3300::aid-chem3300>3.0.co;2-o

Cited by 39 publications

(6 citation statements)

References 25 publications

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“…The opposite diastereomer 5.2a was prepared in 30% de when the ring closure reaction of complex 4a was mediated by KHMDS at −78 °C (entry 1, Table ). Application of t -BuOLi, chiral alkoxide bases (potassium (1 R ,2 S )- or (1 S ,2 R )-[ α -[1-(dimethylamino)ethyl]benzenemethoxide), LiHMDS, NaHMDS, and variations in the nature of solvents (benzene) and additives (AgNO 3 ) did not prove effective for the ring closure, or did not significantly improve the observed diastereoselectivities.…”

Section: Resultsmentioning

confidence: 95%

Ligand-Controlled Asymmetric Induction at a Transition Metal-Bonded α-Carbon in Ester and Amide Enolates. Diastereoselective Formation of Oxapalladacycles Applied to the Synthesis of a Chiral Nonracemic 2H-1-Benzopyran

2003

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Stable benzannelated oxapalladacycles [−(P−P)Pd-1-C6H4-2-OCHY−] possessing chiral nonracemic bidentate phosphine ligands, (P−P) = (4S,5S)-(+)-O-isopropylidene-2,3-dihydroxy-1,4-bis(diphenylphosphino)butane ((S,S)-DIOP) or (2S,4S)-(−)-2,4-bis(diphenylphosphino)pentane ((S,S)-BDPP), and a palladium-bonded stereogenic carbon representing an α-carbon in ester (Y = COOEt) or amide (Y = CONEt2) enolates, have been synthesized in diastereomeric excess 46−80% exploiting asymmetric induction from the chiral ligands. The stereoselective event involved an intramolecular displacement of the iodide in complexes (P−P)IPd-1-C6H4-2-OCH2Y by an in situ generated lithium or potassium ester or amide enolate. Only one enantiomer of each ligand was used, and the absolute sense of stereoinduction could be controlled by the choice of the base (t-BuOK or LDA) to afford both diastereomers of each palladacycle in a diastereomerically enriched form. Treatment of the palladacycles with an excess of t-BuOK allowed for further enrichment in the content of “thermodynamic” diastereomers. An X-ray structure of the complex [−((S,S)-BDPP)Pd-1-C6H4-2-(R)-OCHCOOEt−] was obtained. Ligand exchange reactions of the palladacycles with an achiral 1,2-bis(diphenylphosphino)ethane (dppe) ligand afforded enantiomerically enriched palladacycles [−(dppe)Pd-1-C6H4-2-OCHCOOEt−] in the corresponding enantiomeric purities without a loss of the stereochemical information. Reaction of dimethyl acetylenedicarboxylate (dmad) with complex [−((S,S)-DIOP)Pd-1-C6H4-2-OCHCONEt2−], enriched via chromatography to 96% de, afforded (−)-2-N,N-diethylcarbonyl-3,4-bis(methoxycarbonyl)-2H-1-benzopyran in 88.4% ee with only a minimal (8%) racemization of the metal-bonded stereocenter.

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Section: Resultsmentioning

confidence: 95%

Ligand-Controlled Asymmetric Induction at a Transition Metal-Bonded α-Carbon in Ester and Amide Enolates. Diastereoselective Formation of Oxapalladacycles Applied to the Synthesis of a Chiral Nonracemic 2H-1-Benzopyran

2003

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“…In addition to its utilization in organic reactions, the metal-free approach has been investigated in polymer synthesis because of non-metal residue and diverse reaction mechanisms. The generated polymers are desirable for biomedical 3,4 and electronic 5,6 applications. Therefore, it is extremely important to design and explore organo-catalysts that are suitable for polymer synthesis.…”

Section: Introductionmentioning

confidence: 99%

Synthetic and mechanistic aspects of anionic polymerization of methyl methacrylate using tetrabutyl ammonium thioimidate

Zhang

Wang

2021

Journal of Polymer Science

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The tetrabutylammonium salts of ionic organo‐initiator containing N,N'‐diisopropylthiourea (TUA‐1) or N,N'‐diethylthiourea (TUA‐2) serve as inexpensive initiators for the anionic polymerization of methyl methacrylate (MMA) at room temperature. The molecular weights of obtained polymers are in the range of 1500–22,700 g mol−1 and the molecular weight distributions are fairly broad (Đ = 1.9–2.5) in optimized cases. The molar ratio of monomer to initiator can be achieved up to 800. Side‐reactions, for example, backbiting, transfer reactions result in the polymerization being a non‐living manner, thus leading to broad molecular weight distributions of the resulting polymers. The effects of counterion nature were also studied from the polymerization of MMA using TUA‐1 anion with sodium or potassium salts as counterions under identical conditions. Detailed investigation indicates that the polymerization proceeds via a sulfur anion initiated repeated 1,4‐Machael addition. In general, thioimidate initiators induced MMA polymerization feature certain induction periods, which is ascribed to slow addition thioimidate to CC double bond of MMA as a result of low initiator efficiency.

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“…In contrast to this usual idea, Diels–Alder reactions, where chiral Brønsted base (BB) has been employed for activation of diene component11–14 and also for exerting dissymmetric influence on the stereochemical outcome of the reaction, also forms important means of obtaining enantiomerically enriched cyclohexene derivatives. BBs11–17 as catalytic promoters of asymmetric transformations have generated considerable interest in the last few years.…”

Section: Introductionmentioning

confidence: 99%

Asymmetric Diels–Alder reaction involving chiral benzimidazoles as organocatalysts

Mirgane

Karnik

2011

Chirality

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New Insights in the Search for Chiral Brønsted Bases

Cited by 39 publications

References 25 publications

Ligand-Controlled Asymmetric Induction at a Transition Metal-Bonded α-Carbon in Ester and Amide Enolates. Diastereoselective Formation of Oxapalladacycles Applied to the Synthesis of a Chiral Nonracemic 2H-1-Benzopyran

Ligand-Controlled Asymmetric Induction at a Transition Metal-Bonded α-Carbon in Ester and Amide Enolates. Diastereoselective Formation of Oxapalladacycles Applied to the Synthesis of a Chiral Nonracemic 2H-1-Benzopyran

Synthetic and mechanistic aspects of anionic polymerization of methyl methacrylate using tetrabutyl ammonium thioimidate

Asymmetric Diels–Alder reaction involving chiral benzimidazoles as organocatalysts

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