Journal article
Enhanced reactivity in radical cyclizations of hydrazones using the silicon-tethered 1-bromovinyl group
Tetrahedron, Vol.63(19), pp.3964-3972
2007
DOI: 10.1016/j.tet.2007.03.017
Abstract
A silicon-tethered 1-bromovinyl group was shown to function as a radical precursor for tin-mediated vinyl additions to chiral α- or β-hydroxyhydrazone. In contrast to related thiyl-mediated methods, these vinyl bromides were not limited to the 5- exo cyclization mode. A series of Si-tethered 5- exo and 6- exo cyclizations formed the corresponding five- and six-membered exo-methylene-substituted oxasilacycles. Treatment with fluoride cleaved the Si–C and Si–O bonds to afford the corresponding allylic hydrazines. Diastereoselectivities ranged from 2:1 to 25:1 ( anti: syn) for the 5- exo cyclizations, depending on the size of the exocyclic substituent, but 6- exo cyclization was not diastereoselective. A variant involving Tamao oxidation of the exo-methylene oxasilacyclopentane intermediate afforded a methyl ketone, a net process corresponding to addition of a radical acyl anion equivalent. Bromovinyl radical precursors offer enhanced reactivity in Si-tethered radical addition to hydrazones, enabling application via 6- exo cyclization modes. [Display omitted]
Details
- Title: Subtitle
- Enhanced reactivity in radical cyclizations of hydrazones using the silicon-tethered 1-bromovinyl group
- Creators
- Gregory K FriestadTao JiangAlex K Mathies
- Resource Type
- Journal article
- Publication Details
- Tetrahedron, Vol.63(19), pp.3964-3972
- Publisher
- Elsevier Ltd
- DOI
- 10.1016/j.tet.2007.03.017
- ISSN
- 0040-4020
- eISSN
- 1464-5416
- Language
- English
- Date published
- 2007
- Academic Unit
- Chemistry
- Record Identifier
- 9983985970702771
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