- Cycloadditions of 4-pyrones. An approach to colchicine
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The 4-pyrone, [5-acetoxy-4-oxo-4H-pyran-2-yl]carbonyl chloride was coupled with the malonate anion of bis(2,2,2-trichloroethyl) 2-ethenyl-3,4,5-trimethoxybenzylpropanedioate and analogs thereof. These adducts then underwent intramolecular thermal cyclizations (61-100% yield) to form the two fused seven member rings of the carbon skeleton of colchicine. The malonate moiety was deprotected and decarboxylated quantitatively to provide the desired ring system which contained a bridging ether, from C7a to C11 in the C ring, and a ketone at the 7 position. Removal of the bridging ether as H2O would yield the desired tropolone. Our attempts to remove the ether bridge were unsuccessful.
- McBride,Garst
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p. 2839 - 2854
(2007/10/02)
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- INTRAMOLECULAR CYCLOADDITIONS WITH 2-(ω-ALKENYL)-5-HYDROXY-4-PYRONES
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Five 5-hydroxy-4-pyrones, bearing unsaturated side chains at the 2-position, undergo thermal or acid catalyzed cycloaddition to yield bicycloadducts.
- Garst, Michael E.,McBride, Bill J.,Douglass, James G.
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p. 1675 - 1678
(2007/10/02)
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