ORGN 567 |
| The sage ingredients 7-methoxyrosmanol and galdosol were recently reported to show in vitro affinity to the human brain benzodiazepine receptor. The development of a total synthesis applying the cobalt-mediated [2+2+2] cycloaddition could lead to ways of finding new synthetic abietatriene or abietane diterpenes that may be of pharmacological interest. To achieve this goal, a new variant of the [2+2+2] cycloaddition with cobalt(I) cyclopentadienyl or dicobalt(0) octacarbonyl is applied using alkynyl boronic esters. Their synthetic utility lies in their potential to function as masked hydroxyl groups, giving rise to phenols. Additionally, the boronic ester residues can be substituted by different alkyl groups in Suzuki reactions. Alkynyl boronic esters are also applied to investigate this methodology using the 2,3-double bond of the indole core in an intramolecular [2+2+2] cyclization reaction with the cyclopentadienyl-bis(ethene)cobalt(I) mediator. When isopropylborylacetylene is used for example, complete regioselectivity for the addition of the free alkyne is observed, but interestingly, the syn- as well as the anti-cobalt complex are formed in equal amounts. This reaction is studied in a wide scope in order to get more insight into the reactivity and selectivity of the system. The boron-containing 1,3-dienes are useful starting materials for a large variety of transformations, such as Diels-Alder reactions. Moreover, carbonyl groups are easily accessible from the oxidative replacement of the boronic ester substituents.
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Heterocycles, Aromatics, Metal-Mediated Reactions and Syntheses, Materials, Devices, and Switches
8:00 PM-10:00 PM, Wednesday, 29 March 2006 Georgia World Congress Center -- Ex. Hall B4, Poster
Sci-Mix
Division of Organic Chemistry |
