Theoretical Study of Free-Radical-Mediated 5-<i>exo</i>-Trig Cyclizations of Chiral 3-Substituted Hepta-1,6-dienes

d’Antuono, Philippe; Fritsch, A.; Ducasse, Laurent; Castet, Frédéric; James, Philippe; Landais, Yannick

doi:10.1021/jp0549531

Cited by 9 publications

(10 citation statements)

References 48 publications

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“…[34] EPR experiments were carried out to provide additional information relative to the conformation of radical species I in the ground state. Radical I was generated inside the EPR cavity, at room temperature, by photolytic cleavage of (Bu 3 Sn) 2 in the presence of xanthate 7 and allylsilanes (13 a,d, 14 a, and 17 b) in benzene.…”

Section: Resultsmentioning

confidence: 99%

“…These conformations are similar to those obtained through other spectroscopic methods [36] and in good agreement with our recent calculations on radical cyclizations. [34] To further support the putative conformations of the bsilyl radicals and explain the stereochemistry of the process, we carried out a quantum chemical study on the radical azidation step. The reaction of 1 a with phenylsulfonyl azide to give 9 a was chosen as a model system (see Scheme 6).…”

Section: Resultsmentioning

confidence: 99%

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Carboazidation of Chiral Allylsilanes: Experimental and Theoretical Investigations

Chabaud

Landais

Renaud

et al. 2008

Chemistry A European J

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The carboazidation of chiral allylsilanes has been investigated by varying the nature of the substituents at the silicon center and on the carbon framework. The influence of temperature and the nature of the sulfonyl azide, as well as the stereochemistry of the remote stereogenic center, on the 1,2-diastereocontrol of the process were considered. Good to excellent levels of diastereocontrol were generally observed, with the syn-beta-azidosilane always being formed as the major isomer. An illustration of the value of this methodology has been provided with a short and efficient synthesis of an analogue of castanospermine. EPR spectroscopy was carried out on various beta-silyl radicals providing useful information about their conformations in the ground state. Based on this experimental evidence and DFT calculations, reactant-like transition state models were finally proposed that rationalize the observed 1,2-stereoinduction.

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Section: Resultsmentioning

confidence: 99%

Section: Resultsmentioning

confidence: 99%

Carboazidation of Chiral Allylsilanes: Experimental and Theoretical Investigations

Chabaud

Landais

Renaud

et al. 2008

Chemistry A European J

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“…3 The main characteristics of the reaction were delineated in a seminal article by Beckwith and Ingold in 1980. the cyclohexane ring 2 with the radical centre (X-1) approaching C-5 of the alkene at an angle close to tetrahedral. A number of computational studies of hex-5-enyl ring closures have been reported [20][21][22][23][24] and these have generally supported…”

Section: Introductionmentioning

confidence: 87%

The importance of chain conformational mobility during 5-exo-cyclizations of C-, N- and O-centred radicals

Walton

2014

Org. Biomol. Chem.

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The reaction coordinates of an archetypical set of 5-exo cyclizations of C-, N-and O-centred radicals were investigated by computational methods. G4 theory, and DFT with the um062x functional, were able to rationalise counterintuitive factors such as the 'normal' order of rate constants being: N-centred < C-centred < O-centred radicals. The access angle between the radical centre and the double bond was identified as a key factor. Examination of its evolution during ring closure implied that rigidity at the N-ends of the chains, and the consequent extra energy needed to attain chair-like transition states, might be the reason for slow aminyl cyclizations. A novel linear correlation between cyclization activation energies and the access angles was discovered. The preference for cis-1,2-disubstituted product formation was also accounted for in terms of interaction between the hyperconjugatively delocalized SOMO and the alkene * orbital.

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“…Both of these studies concluded that these exothermic cyclizations were characterized by an early transition state and that exo versus endo selectivity could be attributed to conformational and steric factors in the transition state. More recently, several groups have successfully employed DFT and/or ab initio methods to analyze a variety of radical cyclizations [16][17][18][19]. A few years ago, we reported a kinetic and product study on the cyclization of a series of 4-oxa-5-hexenyl radicals [20].…”

Section: Introductionmentioning

confidence: 99%

Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-Hexenyl and 4-Oxa-5-Hexenyl Radicals

Matlin¹,

Leyden²

2013

IJOC

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The intramolecular cyclization of 5-hexenyl radicals continues to be an important synthetic method for the construction of five-membered rings. The synthetic utility arises from the high degree of regioselectivity to give predominantly cyclopentyl products in high yield under mild conditions. Recently we reported product cyclization studies on 4-oxa perturbed 5-hexenyl radical. In this paper, we report our results from a computational study (UB3LYP and UCCSD (T)) of the cyclization of a series of 5-hexenyl and 3-and 4-oxa-5-hexenyl radicals. Three highly conserved cyclization tran-sitions states (exo-chair, exo-boat and endo-chair) were located for 10 acyclic radicals. Activation energies were calcu-lated for the three modes of cyclization for each radical. Calculated values for the exo/endo cyclization ratios had a high level of agreement with experiment and predictions were offered for two cases that have not been experimentally tested. The increased percentage of exo-cyclization with 3-and 4-oxa substitution is the result of an increase in the energy dif-ference between the exo-and endo-chair transition states compared to the hydrocarbon systems. The decreased rate of cyclization of the 4-oxa compounds is primarily due to the stabilization of the initial acyclic radical by the vinyl ether linkage. The increase in the rate of cyclization with 3-methyl substitution is due to the increased conformational energy of the starting acyclic radical.

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Theoretical Study of Free-Radical-Mediated 5-exo-Trig Cyclizations of Chiral 3-Substituted Hepta-1,6-dienes

Cited by 9 publications

References 48 publications

Carboazidation of Chiral Allylsilanes: Experimental and Theoretical Investigations

Carboazidation of Chiral Allylsilanes: Experimental and Theoretical Investigations

The importance of chain conformational mobility during 5-exo-cyclizations of C-, N- and O-centred radicals

Computational Study of the Cyclization of 5-Hexenyl, 3-Oxa-5-Hexenyl and 4-Oxa-5-Hexenyl Radicals

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