Stereocontrol in Radical Processes through the Exocyclic Effect:  Dual Role of Triethylboron as Radical Initiator and in Situ Derivatization Agent

Bouvier, Jean-Pierre; Jung, Grace; Liu, Ziping; Guérin, Brigitte; Guindon, Yvan

doi:10.1021/ol015758h

Cited by 30 publications

(15 citation statements)

References 14 publications

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“…Taking advantage of this effect allowed for the reliable synthesis of 2,3‐ anti propionate relationships9 found within numerous ionophores bearing tetrahydropyran (THP) rings or tetrahydrofuran rings (THF) 5. 8a–c, e, f…”

Section: Introductionmentioning

confidence: 99%

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Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Godin¹,

Prévost²,

Gorelsky³

et al. 2013

Chemistry A European J

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Radical reductions of halogenated precursors bearing a heterocycle exo (α) to the carbon-centered radical proceed with enhanced anti-selectivity, a phenomenon that we termed "exocyclic effect". New experimental data and DFT calculations at the BHandHLYP/TZVP level demonstrate that the origin of the exocyclic effect is linked to the strain energy required for a radical intermediate to reach its reactive conformation at the transition state (ΔE(≠)(strain)). Furthermore, radical reductions of constrained THP systems indicate that high 2,3-anti inductions are reached only when the radical chain occupies an equatorial orientation. Hydride deliveries to different acyclic substrates and calculations also suggest that the higher anti-selectivities obtained with borinate intermediates are not related to the formation of a complex mimicking an exocycle. From a broader standpoint, this study reveals important conformational factors for reactions taking place at a center vicinal to a heterocycle or an α-alkoxy group.

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Section: Introductionmentioning

confidence: 99%

“…(5)] 4f. 8f Aluminum and magnesium Lewis acids, which were demonstrated to allow the formation of endocyclic radical intermediates by complexation of the ester and the C3alcohol group, afforded selectively the complementary 2,3‐ syn inductions [Eq. (6)] 4a,f.…”

Section: Introductionmentioning

confidence: 99%

Diastereoselective Hydrogen‐Transfer Reactions: An Experimental and DFT Study

Godin¹,

Prévost²,

Gorelsky³

et al. 2013

Chemistry A European J

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“…Guindon and co-workers observed a similar in situ protection of 1,3-diols as boronic esters using Et 3 B and air during the generation of -ester radicals. 42 However, the mechanism of formation of the cyclic boronic ester was not elucidated. Interestingly, only one equivalent of Et 3 B was necessary to protect the 1,3-diol moiety and to initiate the ATRA process.…”

Section: Methodsmentioning

confidence: 99%

Forskolin Editing via Radical Iodo- and Hydroalkylation

et al. 2021

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The modification of highly oxygenated forskolin as well as manoyl and epi-manoyl oxide, two less functionalized model substrates sharing the same polycyclic skeleton, via intermolecular carbon-centered radical addition to the vinyl moiety has been investigated. Highly regio- and reasonably stereoselective iodine atom transfer radical addition (ATRA) reactions were developed. Unprotected forskolin afforded an unexpected cyclic ether derivative. Protection of the 1,3-diol as an acetonide led the formation of the iodine ATRA product. Interestingly, by changing the mode of initiation of the radical process, in situ protection of the forskolin 1,3-diol moiety as a cyclic boronic ester took place during the iodine ATRA process without disruption of the radical chain process. This very mild radical-mediated in situ protection of 1,3-diol is expected to be of interest for a broad range of radical and non-radical transformations. Finally, by using our recently developed tert-butylcatechol-mediated hydroalkylation procedure, highly efficient preparation of forskolin derivatives bearing an extra ester or sulfone group was achieved.

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“…Scheme 12 (eq. A) illustrates this approach, where a diol was initially treated with an excess of Et 3 B, which served the dual role of a free radical initiator and a reagent leading to the cyclic borinate adduct 23 [29]. This Acyclic substituent to the radical Cyclic substituent to the radical antiproduct synproduct borinate was first reduced with Bu 3 SnH and then hydrolyzed in the ensuing work-up step.…”

Section: A Suitably Flanked Carbon-centered Free Radicalmentioning

confidence: 99%