Controlling the regiochemistry of radical cyclizations

Ishibashi, Hiroyuki

doi:10.1002/tcr.20069

Cited by 61 publications

(26 citation statements)

References 39 publications

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“…While these reactions are considered unfavorable due to the difficulty in reaching the Burgi‐Dunitz trajectories for the endo ring closures, a number of examples of nucleophilic closures, along with a few of radical cyclizations, of this type are known . A new explanation for the unusual features of anionic 5‐endo cyclizations came from computational analysis of the parent anionic cyclizations . It was revealed that the TSs for 5‐endo‐dig and 5‐endo‐trig anionic ring closures are stabilized by the presence of a 5c,6e σ‐aromatic orbital array involving the lone pair at the nucleophilic center, the target alkyne (or alkene) π bond, and a σ CC bridge (Figure ).…”

Section: Experimental Evidence: Exo‐digonal Closures Of Small Cyclesmentioning

confidence: 99%

The Baldwin rules: revised and extended

Gilmore

Mohamed

Alabugin

2016

WIREs Comput Mol Sci

135

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The Baldwin rules constitute one of the clearest examples of the success which can be obtained through the application of stereoelectronic concepts to reaction design. With thousands of examples, the predictive power of these rules is inarguable. However, time has revealed a number of exceptions and gray areas within these rules, leading to extensions and revisions. In this review, we will present an overview of how subsequent studies of ring closure have clashed with several of Baldwin's predictions, leading to the revision of some classes of ring closure (alkyne cyclizations, electrophilic closures, etc.). We also discuss for which the original rules were vague (epoxides) or absent (promoted cyclizations), and the evidence revealed since Baldwin's work that has allowed for a better understanding of these ambiguities. With the concise summation of these amendments, this review aims to present an overview of the understanding of cyclization reactions to date. For further resources related to this article, please visit the WIREs website

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Section: Experimental Evidence: Exo‐digonal Closures Of Small Cyclesmentioning

confidence: 99%

The Baldwin rules: revised and extended

Gilmore

Mohamed

Alabugin

2016

WIREs Comput Mol Sci

135

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“…In addition, switching from the 1,6‐diene within 24 to a 1,5‐diene in our new substrate (i.e. 26 ) was hoped to favor cyclization …”

Section: Resultsmentioning

confidence: 99%

N‐Heterocyclic Carbene Catalyzed (5+1) Annulations Exploiting a Vinyl Dianion Synthon Strategy

et al. 2019

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Direct polarity inversion of conjugate acceptors provides av aluable entry to homoenolates.N -heterocyclic carbene (NHC) catalyzedr eactions,i nw hich b-unsubstituted conjugate acceptors undergo homoenolate formation and C À C bond formation twice,h ave been developed. Specifically,t he all-carbon (5+ +1) annulations give ar ange of mono-and bicyclic cyclohexanones (31 examples). In the first family of annulations, b-unsubstituted acrylates tethered to ad ivinyl ketone undergo cycloisomerization, providing hexahydroindenes and tetralins.I nt he second, partially untethered substrates undergo an intermolecular (5+ +1) annulation involving dimerization followed by cycloisomerization. While enantioselectivity was not possible with the former,t he latter proved viable,a llowing cyclohexanones to be produced with high levels of enantiopurity (most > 95:5 e.r.)a nd exclusive diastereoselectivity (> 20:1 d.r.). Derivatizations and mechanistic studies are also reported. Scheme 1. Backgrounda nd mechanistic framework. EWG = electronwithdrawinggroup.Supportinginformation and the ORCID identification number(s) for the author(s) of this article can be found under: https://doi.

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“…Depending on the substitution pattern of the alkene moiety, two cyclization pathways may predominate, respectively. For terminal alkene substrate 2ab and 2ah and internal alkene substrate 2aj , the 5-exo-trig cyclization pathway is kinetically favored 64 , 65 . However, for aryl and alkenyl-substituted alkene substrates, the 6-endo-trig pathway is likely favored due to the stabilization of the resultant radical via conjugation 66 , 67 .…”

Section: Resultsmentioning

confidence: 99%

Radical asymmetric intramolecular α-cyclopropanation of aldehydes towards bicyclo[3.1.0]hexanes containing vicinal all-carbon quaternary stereocenters

Liu

Tian

et al. 2018

Nat Commun

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The development of a general catalytic method for the direct and stereoselective construction of cyclopropanes bearing highly congested vicinal all-carbon quaternary stereocenters remains a formidable challenge in chemical synthesis. Here, we report an intramolecular radical cyclopropanation of unactivated alkenes with simple α-methylene group of aldehydes as C1 source via a Cu(I)/secondary amine cooperative catalyst, which enables the single-step construction of bicyclo[3.1.0]hexane skeletons with excellent efficiency, broad substrate scope covering various terminal, internal alkenes as well as diverse (hetero)aromatic, alkenyl, alkyl-substituted geminal alkenes. Moreover, this reaction has been successfully realized to an asymmetric transformation, providing an attractive approach for the construction of enantioenriched bicyclo[3.1.0]hexanes bearing two crucial vicinal all-carbon quaternary stereocenters with good to excellent enantioselectivity. The utility of this method is illustrated by facile transformations of the products into various useful chiral synthetic intermediates. Preliminary mechanistic studies support a stepwise radical process for this formal [2 + 1] cycloaddition.

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Controlling the regiochemistry of radical cyclizations

Cited by 61 publications

References 39 publications

The Baldwin rules: revised and extended

The Baldwin rules: revised and extended

N‐Heterocyclic Carbene Catalyzed (5+1) Annulations Exploiting a Vinyl Dianion Synthon Strategy

Radical asymmetric intramolecular α-cyclopropanation of aldehydes towards bicyclo[3.1.0]hexanes containing vicinal all-carbon quaternary stereocenters

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