Chiral Brønsted acid-catalyzed enantioselective ionic [2+4] cycloadditions

Borovika, Alina; Nagorny, Pavel

doi:10.1016/j.tet.2013.03.086

Cited by 34 publications

(12 citation statements)

References 54 publications

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“…It is noteworthy that 3 and 4 are cationic in nature and could be viewed as oxocarbenium ions with reactivities similar to those of unsaturated acetal‐derived oxocarbenium ions ( 2 ). While indeed a number of synthetically useful transformations involving the generation of 2 from 1 are known,3 the existing asymmetric methods typically rely on the use of chiral auxiliaries4, 5 and only one recent report from our group7a suggests that such transformations are amenable to asymmetric catalysis.…”

Section: Initial Screen and Reaction Optimizationmentioning

confidence: 99%

Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies

et al. 2014

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An enantioselective intramolecular chiral phosphoric acid‐catalyzed cyclization of unsaturated acetals has been utilized for the synthesis of functionalized chiral piperidines. The chiral enol ether products of these cyclizations undergo subsequent in situ enantioenrichment through acetalization of the minor enantiomer. A new computational reaction exploration method was utilized to elucidate the mechanism and stereoselectivity of this transformation. Rather than confirming the originally postulated cyclization proceeding directly through a vinyl oxocarbenium ion, simulations identified an alternative two‐step mechanism involving the formation of a mixed chiral phosphate acetal, which undergoes a concerted, asynchronous SN2′‐like displacement to yield the product with stereoselectivity in agreement with experimental observations.

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Section: Initial Screen and Reaction Optimizationmentioning

confidence: 99%

Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies

et al. 2014

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“…3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 lene)dimethylammonium chloride, generated in situ from oxalyl chloride and DMF, [26] to obtain the corresponding phosphorochloridate (+)-14 a. Attempts to introduce the N-triflyl phosphoramide function directly from phosphorochloridate (+)-14 a with trifluoromethanesulfonamide, in standard conditions [20b, 25] or in basic media [27] failed. Thus, we considered then a two-step procedure: we reacted (+)-14 a with a large excess of liquid ammonia, [28] which delivered the phosphoramidate (+)-15 a in high yield (86%).…”

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confidence: 99%

Silyl‐Substituted Planar Chiral Phosphoric Acids with Ferrocene‐bridged Paracyclophane Frameworks: Synthesis, Characterization, and Uses in Enantioselective aza‐Friedel‐Crafts Reactions

et al. 2016

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This manuscript reports on a suitable method for the synthesis of paracyclophane type, ferrocene-bridged chiral phosphoric acids, which bear silyl-substituents on their paracyclophane frameworks. These acids have been obtained easily in enantiomerically pure form, by taking advantage of (S)-(1-phenyl-2-cyanoethyl)phosphorodiamidite as a phosphorylating agent. They have been used then as catalysts for aza-Friedel-Crafts reactions between indoles and imines, giving high catalytic activity and up to 98% enantiomeric excess.

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“…[3] Our group is interested in developing organocatalytic transformations involving unsaturated oxocarbenium ions. [4] Among the best known transformations of this type is the ionic [2+4] cycloaddition reaction (Gassman cycloaddition) exemplified by the transformation depicted in Figure 2. [5,6] One of the most popular protocols for such cycloadditions has been developed by the Grieco group and relies on the use of a concentrated lithium(I) perchlorate solution (4.0 m in diethyl ether) and catalytic amounts of sulfonic acids.…”

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Thiophosphoramide‐Based Cooperative Catalysts for Brønsted Acid Promoted Ionic Diels–Alder Reactions

et al. 2013

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Three's a crowd: The combination of a Brønsted acid and a hydrogen‐bond donor cocatalyst was found to promote various ionic [2+4] cycloadditions under mild reaction conditions (see scheme; Ts=4‐toluenesulfonyl). Thiophosphoramides are the most effective cocatalysts because of the stronger counterion activation effect resulting from three, rather than two, hydrogen bonds involved in anion binding.

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Chiral Brønsted acid-catalyzed enantioselective ionic [2+4] cycloadditions

Cited by 34 publications

References 54 publications

Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies

Enantioselective Synthesis of Piperidines through the Formation of Chiral Mixed Phosphoric Acid Acetals: Experimental and Theoretical Studies

Silyl‐Substituted Planar Chiral Phosphoric Acids with Ferrocene‐bridged Paracyclophane Frameworks: Synthesis, Characterization, and Uses in Enantioselective aza‐Friedel‐Crafts Reactions

Thiophosphoramide‐Based Cooperative Catalysts for Brønsted Acid Promoted Ionic Diels–Alder Reactions

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