Everything about Tropinone totally explained
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Tropinone is an
alkaloid, famously synthesised in 1917 by
Robert Robinson as a
synthetic precursor to
atropine, a scarce commodity during
World War I. Tropinone and the alkaloids
cocaine and atropine all share the same
tropane core structure.
Synthesis
The first synthesis of tropinone was by
Richard Willstätter in 1901. It started from the seemingly related
cycloheptanone, but required many steps and had an overall yield of only 0.75%. Willstätter had previously synthesized cocaine from tropinone, in what was the first synthesis and elucidation of the structure of cocaine.
The 1917 synthesis by Robinson is considered a legend in
total synthesis due to its simplicity and biomimetic approach. Tropinone is a
bicyclic molecule, but the
reactants used in its preparation are fairly simple:
succinaldehyde,
methyl amine and
acetone dicarboxylic acid (or even
acetone). The synthesis is a good example of a
biomimetic reaction or
biogenetic-type synthesis because
biosynthesis makes use of the same building blocks. It also demonstrates a
tandem reaction in a
one-pot synthesis. Furthermore the yield of the synthesis was 17% and with subsequent improvements exceeded 90%.
Reaction mechanism
The main features apparent from the reaction sequence below are:
- Nucleophilic addition of secondary amine to aldehyde followed by loss of water to create an imine
- Nucleophilic addition of the imine to the second aldehyde unit and first ring closure
- Intermolecular Mannich reaction of the enolate of actone dicarboxylate
- New enolate formation and new imine formation with loss of water for
- Second intramolecular mannich reaction and second ring closure
- Loss of 2 carboxylic groups to tropinone
Further Information
Get more info on 'Tropinone'.
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