Diastereoselective [4+3] Cycloadditions of Enantiopure Nitrogen‐Stabilized Oxyallyl Cations

MaGee, David I.; Godineau, Edouard; Thornton, Paul D.; Walters, Michael A.; Sponholtz, Deborah J.

doi:10.1002/ejoc.200600226

Cited by 34 publications

(15 citation statements)

References 45 publications

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“…11 Hoffmann studied the asymmetric (4+3) cycloadditions of oxygen-stabilized oxyallyl cations generated from 10 by treatment with TMSOTf; their cycloadditions with 3-substituted furans led predominantly to anti-I adducts. 12 These results have recently been shown to conform to a CH–π mode of stereoinduction similar to that proposed for our oxyallyls 2 .…”

Section: Introductionmentioning

confidence: 99%

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

et al. 2011

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A systematic investigation of the regioselectivities and stereoselectivities of (4+3) cycloadditions between unsymmetrical furans and a chiral oxazolidinone-substituted oxyallyl is presented. Cycloadditions were performed using an oxyallyl containing a (R)-4-phenyl-2-oxazolidinone auxiliary (2Ph), under either thermal or ZnCl2-catalyzed conditions. Reactions of 2Ph with 2-substituted furans gave syn cycloadducts selectively, while cycloadditions with 3-substituted furans gave selectively anti cycloadducts. The stereoselectivities were in favor of a single diastereoisomer (I) in all but one case (2-CO2R). Density functional theory calculations were performed to explain the selectivities. The results support a mechanism in which all cycloadducts are formed from the E isomer of the oxyallyl (in which the oxazolidinone C=O and oxyallyl oxygen are anti to each other) or the corresponding E ZnCl2 complex. The major diastereomer is derived from addition of the furan to the more crowded face of the oxyallyl. Crowded transition states are favored because they possess a stabilizing CH–π interaction between the furan and the Ph group.

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Section: Introductionmentioning

confidence: 99%

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

et al. 2011

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“…6,7 This sequence is a valuable synthetic procedure for formation of 7-membered carbocycles, 8,9 which had previously been achieved using various other chiral, donor-substituted oxyallyl cations. 10,11 Use of 4-phenyloxazolidinone as the auxiliary (R = Ph) provided the diastereomeric endo cycloadducts I and II in a ratio of 82:18, 12 and the ratio increased to ≥96:4 when ZnCl 2 was included in the reaction mixture. 6 …”

Section: Introductionmentioning

confidence: 99%

Stereoselectivity in oxyallyl–furan (4 + 3) cycloadditions: control of intermediate conformations and dispersive stabilisation in cycloadditions involving oxazolidinone auxiliaries

et al. 2010

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Chiral oxazolidinones were previously thought to control cycloaddition stereoselectivity by steric crowding of one face of the substrate. We have discovered that in 4+3 cycloaddition reactions of oxallyls, the stereoinduction is caused instead by stabilising CH–π interactions that lead to reaction at the more crowded face of the oxazolidinone. Density functional theory calculations on the 4+3 cycloadditions of oxazolidinone-substituted oxyallyls with furans establish unexpected transition state conformations and a new explanation of selectivity.

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“…23 As shown in Table 2 , reaction of chiral bromoketone 39 with furan or cyclopentadiene under the standard conditions gave cycloadducts 40a and 40b in approximately a 2:1 ratio favoring the endo-I product.…”

Section: Amido-stabilized Oxyallyl Cations In (4 + 3) Cycloadditionsmentioning

confidence: 98%

“…16,23,24 However, there have been few systematic studies concerning the regioselectivity of oxyallyls and the influence of substituents on the diene. 3e,23 Furthermore, there had not been any coherent let alone predictive model reported for the regioselectivities in (4 + 3) cycloadditions.…”

Section: First Regiochemical Models In Oxyallyl Cation (4 + 3) Cycloamentioning

confidence: 99%

(4+3) Cycloaddition Reactions of Nitrogen‐Stabilized Oxyallyl Cations

Lohse

Hsung

2011

Chemistry A European J

207

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The use of heteroatom-substituted oxyallyl cations in (4 + 3) cycloadditions has had a tremendous impact on the development of cycloaddition chemistry. Extensive efforts have been exerted toward investigating the effect of oxygen-, sulfur-, and halogen-substituents on the reactivity of oxyallyl cations. Most recently, the use of nitrogen-stabilized oxyallyl cations has gained prominence in the area of (4 + 3) cycloadditions. The following article will provide an overview of this concept utilizing nitrogen-stabilized oxyallyl cations.

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Diastereoselective [4+3] Cycloadditions of Enantiopure Nitrogen‐Stabilized Oxyallyl Cations

Cited by 34 publications

References 45 publications

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

Stereoselectivities and Regioselectivities of (4 + 3) Cycloadditions Between Allenamide-Derived Chiral Oxazolidinone-Stabilized Oxyallyls and Furans: Experiment and Theory

Stereoselectivity in oxyallyl–furan (4 + 3) cycloadditions: control of intermediate conformations and dispersive stabilisation in cycloadditions involving oxazolidinone auxiliaries

(4+3) Cycloaddition Reactions of Nitrogen‐Stabilized Oxyallyl Cations

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