Polar [.pi.4 + .pi.2] cycloaddition reaction. Enamines as dipolarophiles in 1,3-dipolar additions

Meilahn, Marcus K.; Cox, Bruce; Munk, Morton E.

doi:10.1021/jo00895a001

Cited by 29 publications

(12 citation statements)

References 7 publications

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“…There appears to be a small solvent effect as compared to the gas phase for the greatly charge separated transition states, TS(1a → 3a) and TS(2 → 5) , but the activation barriers are higher for the unfavored transition states in the gas phase. This result is consistent with the similar experimental rates determined by Munk et al in chloroform and ethanol …”

Section: Resultssupporting

confidence: 94%

“…This paper describes a theoretical exploration of a different type of azide cycloaddition, involving very nucleophilic enamines that react rapidly with the relatively electrophilic azides. Through measurements of solvent effects on rate constants, Hammett parameters, and semiempirical Complete Neglect of Differential Overlap (CNDO) molecular orbital calculations, Munk et al deduced that the reactions involve a concerted mechanism with highly asynchronous transition states …”

Section: Introductionmentioning

confidence: 99%

“…Munk et al performed the reactions and found that 3a – c and 5 were formed exclusively. The reactions were performed in chloroform, ethanol, and acetonitrile, and only minor variations in reaction rates were observed . We have investigated the mechanisms and regioselectivities of the enamine–azide cycloadditions studied by Munk.…”

Section: Introductionmentioning

confidence: 99%

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Mechanisms and Transition States of 1,3-Dipolar Cycloadditions of Phenyl Azide with Enamines: A Computational Analysis

2013

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The transition structures for the 1,3-dipolar cycloadditions of phenyl azide to enamines derived from acetophenone or phenylacetaldehyde and piperidine, morpholine, or pyrrolidine were located using quantum mechanical methods. These cycloadditions were studied experimentally in 1975 by Meilahn, Cox, and Munk (J. Org. Chem. 1975, 40, 819–823). Calculations were carried out with M06-2X/6-311+G(d,p), SCS-MP2/6-311+G(d,p)//M06-2X/6-311+G(d,p), and B97D/6-311+G(d,p) methods with the IEF-PCM solvation model for chloroform and ethanol. The distortion/interaction model was utilized to understand mechanisms, reactivities, and selectivities.

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Section: Resultssupporting

confidence: 94%

Section: Introductionmentioning

confidence: 99%

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Mechanisms and Transition States of 1,3-Dipolar Cycloadditions of Phenyl Azide with Enamines: A Computational Analysis

2013

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“…In the transition state, the destabilization due to disturbing the amino resonance is more effective than the stabilization by the M-effect of the phenyl group. Similar reactivity ratios were found for a-and b-aminostyrenes in 1,3-dipolar cycloadditions of phenyl azide [12] and Diels ± Alder reactions with 3,6-diphenyl-1,2,4,5-tetrazine [15] (Table 7). -NMe 2 1 8…”

Section: Discussionsupporting

confidence: 71%

Structure–Nucleophilicity Relationships for Enamines

Kempf

Hampel

Ofial

et al. 2003

Chemistry A European J

196

115

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The kinetics of the reactions of benzhydryl cations with 22 enamines, three pyrroles, and three indoles were investigated photometrically in dichloromethane. The nucleophilicity parameters N and slope parameters s of these electron-rich pi-systems were derived from equation log k (20 degrees C)=s(E+N) and compared with the nucleophilicities of other pi-systems (silyl enol ethers, silyl ketene acetals) and carbanions. It is shown that the nucleophilic reactivities of enamines cover more than ten orders of magnitude, comparable to enol ethers on the low reactivity end and to carbanions on the high reactivity end. Since the products of N-attack are thermodynamically less stable than the reactants, the observed rate constants refer to the formation of the carbon bond;carbon bonds. In some cases, equilibrium constants for the formation of iminium ions were measured, which allow one to determine the intrinsic rate constants of these reactions.

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“…The rate constant for the cycloaddition of 4-nitroperfluorophenyl azide ( d ) and 5 is 1.216 ± 0.032 M −1 s −1 , which is the fastest for the cycloaddition of an azide with an unstrained dipolarophile. The mechanism of 1,3-dipolar cycloadditions involving enamines and phenyl azide has been explored experimentally by Munk 12 and computationally by Houk. 13 The rate constants of the cycloaddition between PFAA ( a, b ) and enamine ( 5−8 ) were subsequently measured and are summarized in Table 3.…”

Section: Resultsmentioning

confidence: 99%

1,3-Dipolar Cycloaddition Reactivities of Perfluorinated Aryl Azides with Enamines and Strained Dipolarophiles

et al. 2015

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The reactivities of enamines and predistorted (strained) dipolarophiles toward perfluoroaryl azides (PFAAs) were explored experimentally and computationally. Kinetic analyses indicate that PFAAs undergo (3 + 2) cycloadditions with enamines up to 4 orders of magnitude faster than phenyl azide reacts with these dipolarophiles. DFT calculations were used to identify the origin of this rate acceleration. Orbital interactions between the cycloaddends are larger due to the relatively low-lying LUMO of PFAAs. The triazolines resulting from PFAA–enamine cycloadditions rearrange to amidines at room temperature, while (3 + 2) cycloadditions of enamines and phenyl azide yield stable, isolable triazolines. The 1,3-dipolar cycloadditions of norbornene and DIBAC also show increased reactivity toward PFAAs over phenyl azide but are slower than enamine–azide cycloadditions.

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Polar [.pi.4 + .pi.2] cycloaddition reaction. Enamines as dipolarophiles in 1,3-dipolar additions

Cited by 29 publications

References 7 publications

Mechanisms and Transition States of 1,3-Dipolar Cycloadditions of Phenyl Azide with Enamines: A Computational Analysis

Mechanisms and Transition States of 1,3-Dipolar Cycloadditions of Phenyl Azide with Enamines: A Computational Analysis

Structure–Nucleophilicity Relationships for Enamines

1,3-Dipolar Cycloaddition Reactivities of Perfluorinated Aryl Azides with Enamines and Strained Dipolarophiles

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