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Functionalisation of terpenoids at C-4 via organopalladium dimers: cyclopropane formation during oxidation of homoallylic sigma-organopalladium intermediates with lead tetraacetate

Ramos, SS; Almeida, P; Santos, L; Motherwell, WB; Sheppard, TD; Costa, MD; (2007) Functionalisation of terpenoids at C-4 via organopalladium dimers: cyclopropane formation during oxidation of homoallylic sigma-organopalladium intermediates with lead tetraacetate. TETRAHEDRON , 63 (51) 12608 - 12615. 10.1016/j.tet.2007.10.016. Green open access

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Abstract

The synthesis of new potential adjuvant saponin aglycons was investigated by selective palladium mediated C-H functionalisation of appropriately functionalised derivatives of lanosterol, cholesterol, and friedelin. The desired equatorial aldehyde functionality was successfully introduced into the lanosterol skeleton as expected. Cyclopalladation of a cholesterol derivative proceeded as expected, but during oxidation of the organopalladium intermediate, participation of the adjacent alkene functionality led to stereoselective formation of a cyclopropane and introduction of an acetate group into the steroid backbone at C-6. Further investigation of this unusual cyclopropane formation on a model decalin system confirmed the result, but C-H activation on a related open chain system was prevented by complexation of the alkene functionality to the palladium. (c) 2007 Elsevier Ltd. All rights reserved.

Type: Article
Title: Functionalisation of terpenoids at C-4 via organopalladium dimers: cyclopropane formation during oxidation of homoallylic sigma-organopalladium intermediates with lead tetraacetate
Open access status: An open access version is available from UCL Discovery
DOI: 10.1016/j.tet.2007.10.016
Publisher version: http://dx.doi.org/10.1016/j.tet.2007.10.016
Language: English
Keywords: SAPONINS
UCL classification: UCL > Provost and Vice Provost Offices
UCL > Provost and Vice Provost Offices > UCL BEAMS
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences
UCL > Provost and Vice Provost Offices > UCL BEAMS > Faculty of Maths and Physical Sciences > Dept of Chemistry
URI: http://discovery.ucl.ac.uk/id/eprint/170115
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