Cooperative Lewis acid–onium salt catalysis as tool for the desymmetrization of meso-epoxides

Broghammer, Florian; Brodbeck, Daniel; Junge, Thorsten; Peters, René

doi:10.1039/c6cc09774j

Cited by 29 publications

(16 citation statements)

References 50 publications

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“…To demonstrate the synthetic utility of the reaction, different transformations of the aminoazidation product ( 8 ) were performed (Scheme 3). Click reactions of 8 with terminal [21d, 28] or internal alkynes, [29] a benzyne precursor, [30] or acetylacetone [31] afforded the corresponding triazoles ( 57 – 62 ) with good yields and without loss of enantioselectivity. The chiral azide ( 8 ) was reduced in 79 % yield to the corresponding chiral primary amine ( 63 ) by refluxing the chlorophenyl compound ( 8 ) with indium powder in MeOH [32] .…”

Section: Resultsmentioning

confidence: 99%

Iron‐Catalyzed Radical Asymmetric Aminoazidation and Diazidation of Styrenes

Sun

Zhou

et al. 2021

Angew Chem Int Ed

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Asymmetric aminoazidation and diazidation of alkenes are straightforward strategies to build value‐added chiral nitrogen‐containing compounds from feedstock chemicals. They provide direct access to chiral organoazides and complement enantioselective diamination. Despite the advances in non‐asymmetric reactions, asymmetric aminoazidation or diazidation based on acyclic systems has not been previously reported. Here we describe the iron‐catalyzed intermolecular asymmetric aminoazidation and diazidation of styrenes. The method is practically useful and requires relatively low loading of catalyst and chiral ligand. With mild reaction conditions, the reaction can be completed on a 20 mmol scale. Studies of the mechanism suggest that the reaction proceeds via a radical pathway and involves stereocontrol of an acyclic free radical which probably takes place through a group transfer mechanism.

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Section: Resultsmentioning

confidence: 99%

Iron‐Catalyzed Radical Asymmetric Aminoazidation and Diazidation of Styrenes

Sun

Zhou

et al. 2021

Angew Chem Int Ed

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“…In CH 2 Cl 2 at −50 °C, the activity and enantioselectivity were low (Table , entry 1). We were studying catalysts bearing only one ammonium bromide salt side chain because (1) we were speculating that a competition between both ammonium moieties might take place and lead to different enantioface differentiations in the 1,2‐addition step and (2) to increase the solubility of the complexes . By this change, the solubility issue was successfully addressed.…”

Section: Resultsmentioning

confidence: 99%

Asymmetric Carboxycyanation of Aldehydes by Cooperative AlF/Onium Salt Catalysts: from Cyanoformate to KCN as Cyanide Source

Brodbeck

Álvarez‐Barcia

Meisner

et al. 2019

Chemistry A European J

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Asymmetric 1,2‐additions of cyanide yield enantioenriched cyanohydrins as versatile chiral building blocks. Next to HCN, volatile organic cyanide sources are usually used. Among them, cyanoformates are more attractive on technical scale than TMSCN for cost reasons, but catalytic productivity is usually lower. Here, the development of a new strategy for cyanations is described, in which this activity disadvantage is overcome. A Lewis acidic Al center cooperates with an aprotic onium moiety within a remarkably robust bifunctional Al–F–salen complex. This allowed for unprecedented turnover numbers of up to 104. DFT studies suggest an unexpected unique trimolecular pathway in which the ammonium bound cyanide attacks the aldehyde, which itself is activated by the carbonyl group of the cyanoformate binding to the Al center. In addition, a novel practical carboxycyanation method was developed that makes use of KCN as the sole cyanide source. The use of a pyrocarbonate as carboxylating reagent provided the best results.

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“…Some years ago we introduced the concept of asymmetric bifunctional Lewis acid/aprotic onium salt catalysis and since then this concept has demonstrated its potential in various reaction classes such as [2+ +2] cycloadditions, [5] S N reactions [6] and 1,2-additions. [7] Thesynthetic transformations investigated were either previously not viable or not very efficient in terms of catalytic activity.Herein we report that this concept allows for extraordinary catalytic activity combined with high enantioselectivity in the hydroboration of ketones,a llowing for TONs up to 15 400, being equivalent to an increase of activity of about 1.5 to > 3orders of magnitude compared to the most efficient asymmetric hydroboration catalysts.O ur development was driven by the idea that aL ewis acidic oxophilic metal center could activate ak etone substrate, whereas ab orane reagent might be activated by an appended ammonium halide moiety via aboron/halide interaction (Scheme 1).…”

Section: Introductionmentioning

confidence: 99%

Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones

et al. 2021

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Enantiopure secondary alcohols are fundamental high-value synthetic building blocks.One of the most attractive ways to get access to this compound class is the catalytic hydroboration. We describe an ew concept for this reaction type that allowed for exceptional catalytic turnover numbers (up to 15 400), which were increased by around 1.5-3 orders of magnitude compared to the most active catalysts previously reported. In our concept an aprotic ammonium halide moiety cooperates with an oxophilic Lewis acid within the same catalyst molecule.C ontrol experiments reveal that both catalytic centers are essential for the observed activity.Kinetic, spectroscopic and computational studies show that the hydride transfer is rate limiting and proceeds via ac oncerted mechanism, in whichh ydride at Boron is continuously displaced by iodide,r eminiscent to an S N 2r eaction. The catalyst, whichi s accessible in high yields in few steps,w as found to be stable during catalysis,r eadily recyclable and could be reused 10 times still efficiently working.

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Cooperative Lewis acid–onium salt catalysis as tool for the desymmetrization of meso-epoxides

Cited by 29 publications

References 50 publications

Iron‐Catalyzed Radical Asymmetric Aminoazidation and Diazidation of Styrenes

Iron‐Catalyzed Radical Asymmetric Aminoazidation and Diazidation of Styrenes

Asymmetric Carboxycyanation of Aldehydes by Cooperative AlF/Onium Salt Catalysts: from Cyanoformate to KCN as Cyanide Source

Highly Active Cooperative Lewis Acid—Ammonium Salt Catalyst for the Enantioselective Hydroboration of Ketones

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