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

Matlin, Albert R.; Leyden, Matthew C.

doi:10.4236/ijoc.2013.33021

Cited by 3 publications

(7 citation statements)

References 23 publications

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“…Table shows that although the calculated transition state free energies for cyclization of radicals 13 and 14 are slightly different from those reported in the literature, − they all follow the same expected trends; that is a lower transition state free energy for the 5-exo cyclization of 13 than for the 6-exo cyclization of 14 . Both have chairlike transition states and the free energy of the reaction (product) is significantly exergonic in both cases.…”

Section: Results and Discussioncomputationalmentioning

confidence: 46%

“…This has been previously described in the literature as a kinetic effect. 21 Since the substituents increase the number of gauche interactions in the open chain system, both ΔH and − TΔS decrease for the transition state and product. This can also be observed in the less endergonic cyclization reactions of 18 and 19 compared to 17 (Table 3).…”

Section: ■ Results and Discussioncomputationalmentioning

confidence: 99%

“…In order to validate the computational method, four radical cyclization systems were evaluated ( 13 – 16 , Figure ): the 5-exo cyclizations of the 5-hexenyl and 3-phenylpropyl radicals ( 13 and 15 ), and the 6-exo cyclizations of the 6-heptenyl and 4-phenylbutyl radicals ( 14 and 16 ). While 13 and 14 are well studied systems both experimentally and computationally, − there are, to our knowledge, no experimental data for cyclizations of 15 and 16 , with only a few related computational papers having appeared recently. − …”

Section: Results and Discussioncomputationalmentioning

confidence: 99%

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Photoredox Catalyzed Intramolecular Fluoroalkylarylation of Unactivated Alkenes

2017

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The first example of photoredox catalyzed difluoromethylation of unactivated alkenes coupled with C-C bond formation to an aryl ring is reported. The reactions are conducted under mild conditions and afford tetralin derivatives bearing difluoromethyl as well as other fluoroalkyl groups in good to high yields. In addition, the study indicates that 6-exo radical cyclization of an alkyl radical to a phenyl ring is faster than the respective 5-exo radical cyclization. A computational study provides insights to the experimental results.

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Section: Results and Discussioncomputationalmentioning

confidence: 46%

Section: ■ Results and Discussioncomputationalmentioning

confidence: 99%

Section: Results and Discussioncomputationalmentioning

confidence: 99%

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Photoredox Catalyzed Intramolecular Fluoroalkylarylation of Unactivated Alkenes

2017

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“…18,19 For 5-exo-closures this TS resembles the comparatively strain-free chair conformation of 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 Beckwith-Houk type TS models. Computational studies of the ring closures of carbonyl radicals, 25 iminyl radicals, 13 aminyl radicals 26 and oxyl radicals 15 have generally focused either on the exo vs. endo regioselectivity or on details of the stereochemistry induced by substituents.…”

Section: Introductionmentioning

confidence: 85%

“…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: 88%

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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