The rearrangement of a homoallyl cation to a cyclopropylcarbinyl cation is
thought to play a role in the biogenesis of a variety of cyclopropane-containing natural
products,¹ a hypothesis which has previously led to the design of successful
biomimetic syntheses of several natural products.² The strategy underlying this
approach to cyclopropane synthesis³ can be applied more broadly and would be
particularly valuable if it could be extended to a set of contiguous cyclopropanes.
This concept has led us to examine the rearrangement of certain homoallylic
systems bearing a leaving group (triflate) at one terminus and a cation-stabilizing
metal (tin) at the other. The effects of protecting groups of varying steric demand and
of olefin geometry on the stereochemical outcome of the cyclization were examined.
"Zipper" cyclization of (8R,5E,2Z)-1-tri-n-butylstannyl-9-trityloxy-nona-2,5-dien-8-ol
(117) led to the stereoselective formation of three distinct bicyclopropane
stereoisomers (110,111,112). The major diastereomer was isolated through
derivatization and the absolute stereochemistry was verified by X-ray crystallography.
The trans,syn,trans-bicyclopropane 118 was carried forward to complete a formal
synthesis of the antifungal agent FR-900848 (49).
The synthesis of a key precursor to halicholactone (188), neohalicholactone
(189), and the solandelactones A-H (190-197) constructed around a transcyclopropane
core is also described. The key steps in this synthesis are the
stereoselective synthesis of trans-vinylcyclopropane 79, followed by a highly
diastereoselective acetate aldol reaction leading to compound 269. / Graduation date: 2005
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/28965 |
| Date | 07 March 2005 |
| Creators | Lincoln, Christopher M. |
| Contributors | White, James D. |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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