ORGN 7 |
| Due to the unique combination of high reactivity and chirality, functionalized allenes are tremendously useful intermediates in target-oriented synthesis. We are particularly interested in the stereoselective synthesis of alpha- or beta-hetero-substituted allenes and their efficient and stereocontrolled conversion (with axis-to-center chirality transfer) into target molecules of biological and pharmacological interest. For example, treatment of a-hydroxyallenes with catalytic amounts of gold(I) or gold(III) precatalysts affords a smooth access to 2,5-dihydrofurans which can be used for the enantioselective synthesis of mycotoxins (e.g., citreoviral). By fine-tuning of the precatalyst and reaction conditions, the catalyst loading can be reduced to 0.1 mol%, making the method highly competitive with the most efficient processes in homogeneous transition metal catalysis. The method can be applied to the corresponding cycloisomerization of a-aminoallenes to 3-pyrrolines, opening new avenues in alkaloid synthesis. We were also able to establish the first example of a gold-catalyzed C-S bond formation by converting a-thioallenes into 2,5-dihydrothiophenes. |
|
Allenes in Synthesis
8:00 AM-12:00 PM, Sunday, 26 March 2006 Georgia World Congress Center -- C303/304/305, Oral
Division of Organic Chemistry |