- Total synthesis of the spirocyclic oxindole alkaloids corynoxine, corynoxine B, corynoxeine, and rhynchophylline
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Racemic total syntheses of four spirocyclic oxindole alkaloids are reported. The general starting material was an N-2-butenylated 2-hydroxytryptamine, which underwent a base-mediated Mannich spirocyclisation with a functionalised aldehyde to generate the C-ring. The second key step was a Pd-catalysed cyclisation of an α-keto ester enolate (in the original aldehyde) onto an allylic carbonate (in the N-substituent) to form the D-ring. The stereoselectivities of the key steps were moderate, but the isomers were readily purified, so that the natural products could be conveniently prepared, three of them for the first time. Racemic total syntheses of the four title spirocyclic oxindole alkaloids are reported starting from 4-hydroxytryptamine. The key steps were a base-mediated Mannich spirocyclisation to form the C-ring, and a Pd-catalysed cyclisation of a keto ester enolate onto an allylic carbonate to form the D-ring. Thus, convenient syntheses of the alkaloids were achieved, for three of them for the first time. Copyright
- Wanner, Martin J.,Ingemann, Steen,Van Maarseveen, Jan H.,Hiemstra, Henk
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p. 1100 - 1106
(2013/03/29)
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- Process for the production of specific isomer mixtures from oxindole alkaloids
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To produce defined isomer mixtures of compounds with spirocyclic beta-aminocarboxyl and/or beta-aminocarbonyl systems the invention supposes that they be dissolved in solvents which have good dissolving power for these compounds, whose relative permittivity is sufficient to stabilize the amphoteric intermediates occuring in isomerization, which as proton donors constitute hydrogen bridges, whose basicity is less than that of the compounds for isomerization and whose boiling point is so high that an adequate reaction speed can be attained by raising temperature. Further, the invention proposes that the isomerization be prevented, influenced, or terminated by altering at least one of these factors and or by altering the temperature.
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