Aziridine Lithiation Using Lewis Acid Activation

Vedejs, E.; Kendall, John T.

doi:10.1021/ja970164o

Cited by 74 publications

(25 citation statements)

References 28 publications

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“…70 However, ketone 13 was not stable and was immediately carried on to the organometallic addition step. The increased acidity of the α-hydrogens, likely as a consequence of nitrogen complexation, 71 required the use of softer, less Brønsted basic organocerium reagents. 72 The resulting additions took place (40–98% yield) to form 15 { 1–7 } with complete β-diastereoselection as a consequence of the bowl shape of the core scaffold.…”

Section: Resultsmentioning

confidence: 99%

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase-Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

2011

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Despite over three decades of research into asymmetric phase transfer catalysis (APTC), a fundamental understanding of the factors that affect the rate and stereoselectivity of this important process are still obscure. This paper describes the initial stages of a long-term program aimed at elucidating the physical organic foundations of APTC employing a chemoinformatic analysis of the alkylation of a protected glycine imine with a libraries of enantiomerically enriched quaternary ammonium ions. The synthesis of the quaternary ammonium ions follows a diversity oriented approach wherein the tandem inter[4+2]/intra[3+2] cycloaddition of nitroalkenes serves as the key transformation. A two part synthetic strategy comprised of: (1) preparation of enantioenriched scaffolds and (2) development of parallel synthesis procedures is described. The strategy allows for the facile introduction of four variable groups in the vicinity of a stereogenic quaternary ammonium ion. The quaternary ammonium ions exhibited a wide range of activity and to a lesser degree enantioselectivity. Catalyst activity and selectivity are rationalized in a qualitative way based on the effective positive potential of the ammonium ion.

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Section: Resultsmentioning

confidence: 99%

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase-Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

2011

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“…Another recent work demonstrates that this methodology can be successfully applied to the a-alkylation of N-alkylaziridines, [18] and it has been revealed that the incoming substituent preferentially attacks the complex 4 at the syn position relative to the BH 3 ligand (Scheme 3). This stereoselectivity was confirmed in the case of the N-methylisoindole ± borane complex 5.…”

Section: In Memory Of Bob Squiresmentioning

confidence: 99%

Thermochemical Data of Organic Ions Obtained from Investigations in the More or Less “Diluted” Gas Phase

Kuck¹

2000

Angewandte Chemie International Edition

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How is a proton bound to an arene, how mobile is it in such a complex, and how much energy is required to remove it-these questions have been of fundamental interest in physical organic chemistry for half a century. The experimental determination of quantitative thermochemical data of organic elementary processes in the gas phase is discussed for recent examples, such as the alpha-acidification of tertiary amines by complexation with boranes (see reaction) and the "local" C(alpha)-H acidities of alpha,alpha,alpha-trifluoromethylbenzene and higher analogues.

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“…In this paper [4]it was first postulated that carbanions were configurationally stable at low temperatures. In 1997 Vedejs published a paper on lithiated complexes of aziridines with BH 3 [6]. It was shown that the increased s-character of the CH bonds in the aziridine ring accelerated lithiation in position 2 of the aziridine ring, facilitating the reaction with electrophiles.…”

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confidence: 99%

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

Shtrumfs

Hermane

Kalvinsh

et al. 2007

Chem Heterocycl Compd

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A series of N-substituted amides and esters of aziridine-2-carboxylic acids have been prepared and have been subjected to deprotonation with lithium diisopropylamide. The intermediate carbanions reacted more readily with the carbonyl groups of the substrates than with methyl iodide. So, in place of the expected amides or esters of methylaziridine-2-carboxylic acids, amides or esters of 2-aziridinylcarbonylaziridine-2-carboxylic acids were isolated.Keywords: aziridinyl ketones, esters and amides of aziridin-2-carboxylic acids, deprotonation.Esters and amides of aziridine-2-carboxylic acids are suitable starting materials for the preparation of derivatives of α-and β-amino acids after opening the aziridine ring [2,3]. Unlike other esters of α-amino acids, aziridine-2-carboxylates do not have a tendency to dimerize to form diketopiperazines. Our interest in esters and amides of aziridine-2-carboxylic acids is connected with the study of the conditions for deprotonation of the α-center of the aziridine ring to prepare sterically hindered cyclic unnatural α-amino acids, required for the synthesis of different derivatives of α-and β-amino acids.Deprotonation of esters of aziridine-2-carboxylic acid was first carried out by Seebach [4,5]. However isolation of the reaction products was unsuccessful. Only after moving to thiol esters was isolation of the products from the reactions with electrophiles successful [4]. In this paper [4]it was first postulated that carbanions were configurationally stable at low temperatures. In 1997 Vedejs published a paper on lithiated complexes of aziridines with BH 3 [6]. It was shown that the increased s-character of the CH bonds in the aziridine ring accelerated lithiation in position 2 of the aziridine ring, facilitating the reaction with electrophiles.The stability of carbanions in a series of esters of aziridine-2-carboxylic acids has been demonstrated recently [7,8]. A methoxymethyl protecting group on the aziridine nitrogen atom stabilizes the intermediate carbanion and permits the preparation of a series of 2-substituted esters of aziridine-2-carboxylic acids [8]. Alkylation of 3-substituted esters of 1-(diphenylmethyl)aziridine-2-carboxylic acids gave a mixture of 2-alkylated aziridines and diaziridinyl ketones [9].We have studied the deprotonation of derivatives of aziridine-2-carboxylic with different substituents in the aziridine ring to determine the limits of use of this reaction. As substituents we chose well known protecting groups which are readily removed after the reaction was completed. We have developed a method for synthesis of the 1-substituted dimethylamides of the aziridine-2-carboxylic acids 2a-c (scheme 1) required for this study.

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Aziridine Lithiation Using Lewis Acid Activation

Cited by 74 publications

References 28 publications

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase-Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

A Systematic Investigation of Quaternary Ammonium Ions as Asymmetric Phase-Transfer Catalysts. Synthesis of Catalyst Libraries and Evaluation of Catalyst Activity

Thermochemical Data of Organic Ions Obtained from Investigations in the More or Less “Diluted” Gas Phase

Unnatural amino acids. 3. Aziridinyl ketones from esters and amides of aziridine-2-carboxylic acids

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