| dc.contributor.author | Zhao, Liang. | en_US |
| dc.date.accessioned | 2014-10-21T12:36:32Z | |
| dc.date.available | 2006 | |
| dc.date.issued | 2006 | en_US |
| dc.identifier.other | AAINR16721 | en_US |
| dc.identifier.uri | http://hdl.handle.net/10222/54812 | |
| dc.description | The kempanes (e.g. kempene-2 and kempenone) are diterpenes that were isolated from the defense secretions of nasute termites. Due to their potential biological interest and their unique carbon skeleton with a large number of stereogenic centers, attempts have been made to achieve their total synthesis, but only one total synthesis of a kempane has been reported so far. | en_US |
| dc.description | The research described in the this thesis was aimed at using ring-closing-metathesis (RCM) as the key step for the generation of the tetracyclic skeleton. Initial efforts were focused on the construction of a diene bearing an isopropylidene unit on a five-membered ring. An initial aldol approach to this diene gave none of expected product. An alternate route began with a previously prepared lactone. Dehydration was attempted to give the double-bond of the isopropylidene, but a mild selenation and oxidation protocol delivered a tetrafuran as the major product and the expected alkene as a very minor product. Finally, the diene was made using a Mannich route to introduce the isopropylidene unit in high overall yield. An endo-, regio-, and facially selective Diels-Alder reaction of the diene gave a compound with three of the four rings of the kempanes with the key central stereochemistry established. Diastereoselective allylation was tested in a model. Following cerium-mediated, regioselectiye reduction, Grignard allylation, and Dess-Martin oxidation, the RCM worked well to generate the final seven-membered ring. The construction of the tetracyclic skeleton of the kempanes via the RCM reaction was accomplished in 24 steps from commercially available starting materials. Further work to complete the total syntheses of all kempanes is under investigation in this laboratory. | en_US |
| dc.description | This thesis also reports the relative proportions of the products of axial and equatorial 1,2-addition of allylindium, allyl Grignard, and allylbismuth reagents on alpha,beta-conjugated ketones. The diastereoselectivity of allyl Grignard additions was the most selective, favoring axial addition, of the three reagents. | en_US |
| dc.description | Thesis (Ph.D.)--Dalhousie University (Canada), 2006. | en_US |
| dc.language | eng | en_US |
| dc.publisher | Dalhousie University | en_US |
| dc.publisher | | en_US |
| dc.subject | Chemistry, Organic. | en_US |
| dc.title | Toward the total synthesis of the kempanes. | en_US |
| dc.type | text | en_US |
| dc.contributor.degree | Ph.D. | en_US |
