Regiochemistry of intramolecular [2+2] photocycloadditions of oxygenated
6-alkenyl-3-alkoxy-2-cyclohexenones is studied. Application of this methodology
to construct a key intermediate [3.3.2] bicyclic skeleton of ryanodol is described
as well. Irradiation of (3-butenyl)compounds 3, 11, 14 and of (4-pentenyl)compound 6 afforded exclusively the linear photoadducts 4, 12, 15 and
7 respectively. Irradiation of allyl compound 25 brought the desired crossed
photoadduct 26. The structures of the photoadducts 4, 7 and 26 were assigned
based on spectroscopic analysis and confirmed by subsequent retroaldol
cleavage reactions of the corresponding photoproducts. The regiochemistry of
linear adduct 15 was deduced by a sequence of transformations. Retroaldol
cleavage of the photoadduct 15, followed by transannular reductive coupling with
SmI���, and hydrolysis of the protecting group provided triol 18. PDC oxidation of
18 gave [4.2.2] bicyclic triketone 20 and a cyclic hemiketal 21. Finally, Swern
oxidation of 18 confirmed both isomers of photoproduct 15 are linear adducts.
Selective retroaldol ring opening of compound 26 resulted in the formation of the
bicyclo[3.3.1]nonane skeleton, amenable through a one carbon ring expansion to establish the core bicyclo[3.3.2]decane system in ryanodol. / Graduation date: 1998
| Identifer | oai:union.ndltd.org:ORGSU/oai:ir.library.oregonstate.edu:1957/33725 |
| Date | 04 February 1998 |
| Creators | Wang, Bingbing |
| Contributors | Somoza, Carmen |
| Source Sets | Oregon State University |
| Language | en_US |
| Detected Language | English |
| Type | Thesis/Dissertation |
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