Enhanced reactivity in radical cyclizations of hydrazones using the silicon-tethered 1-bromovinyl group

Friestad, Gregory K.; Jiang, Tao; Mathies, Alex K.

doi:10.1016/j.tet.2007.03.017

Cited by 9 publications

(3 citation statements)

References 47 publications

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“…Synthetic applications of radical reactions of N , N -diphenylhydrazones, which are not the subject of the present review, are similar to their N , N -dibenzyl counterparts . It was noted, however, that the electron-rich N , N -dibenzylhydrazones are rather susceptible to elimination of β-hydroxy and β-silyloxy groups …”

Section: Free Radical Reactionsmentioning

confidence: 82%

“…267 It was noted, however, that the electron-rich N,N-dibenzylhydrazones are rather susceptible to elimination of β-hydroxy and β-silyloxy groups. 268 The thiyl radical-initiated addition-cyclization under previously described conditions provided a product of vinyl transfer from silicon to the hydrazone azomethine carbon in 368 (6-exo-cyclization) with almost complete diastereoselectivity (98:2, Scheme 69). The yield was dependent upon the choice of initiator and reaction conditions (10-55%).…”

Section: Radical Addition Of Silicon-tethered Vinyl and Acetylene Groupsmentioning

confidence: 99%

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N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

2009

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Section: Free Radical Reactionsmentioning

confidence: 82%

Section: Radical Addition Of Silicon-tethered Vinyl and Acetylene Groupsmentioning

confidence: 99%

N,N-Dialkylhydrazones in Organic Synthesis. From Simple N,N-Dimethylhydrazones to Supported Chiral Auxiliaries

2009

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“…The construction of carbon−carbon and other bonds is central to organic chemistry and there are many reliable methods that can efficiently achieve these outcomes, involving both ionic and free-radical mediated chemistry. In the free-radical arena the literature abounds with examples for the construction of carbo- and heterocyclic compounds and apart from examples that are affected by unusual orbital interactions, the vast majority of these ring-closures involve intramolecular homolytic addition reactions that are governed by Beckwith−Houk considerations. , …”

Section: Introductionmentioning

confidence: 99%

Multiorbital Interactions during Acyl Radical Addition Reactions Involving Imines and Electron-Rich Olefins

2007

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Ab initio and DFT calculations reveal that acyl radicals add to imines and electron-rich olefins through simultaneous SOMO --> pi*, pi --> SOMO, and HOMO --> pi*C=O interactions between the radical and the radicalophile. At the CCSD(T)/aug-cc-pVDZ//QCISD/cc-pVDZ level, energy barriers of 15.6 and 17.9 kJ mol(-1) are calculated for the attack of the acetyl radical at the carbon and nitrogen ends of methanimine, respectively. These barriers are 17.1 and 20.4 kJ mol(-1) at BHandHLYP/cc-pVDZ. In comparison, barriers of 34.0 and 23.4 kJ mol(-1) are calculated at BHandHLYP/cc-pVDZ for reaction of the acetyl radical at the 1- and 2-positions in aminoethylene, repectively. Natural bond orbital (NBO) analysis at the BHandHLYP/6-311G** level of theory reveals that SOMO --> pi*imine, pi imine--> SOMO, and LPN --> pi*C=O interactions are worth 90, 278, and 138 kJ mol-1, respectively, in the transition state (2) for reaction of acetyl radical at the nitrogen end of methanimine; similar interactions are observed for the chemistry involving aminoethylene. These multiorbital interactions are responsible for the unusual motion vectors associated with the transition states involved in these reactions. NBO analyses for the remaining systems in this study support the hypothesis that the acetyl radical is ambiphilic in nature.

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