A synthesis of the steroidal alkaloid demissidine from epiandrosterone is reported. A ring fragmentation reaction that efficiently ruptured the D-ring of a diazo ester derivative of epiandrosterone to provide an aldehyde tethered ynoate product was key to this sequence. Incorporation of the indolizidine framework was achieved by an azomethine ylide 1,3-dipolar cycloaddition.
A short synthetic sequence
leading to the formation of the C,D,E-ring subunit of the Aspidosperma alkaloids is reported. This route is based
on a ring fragmentation/intramolecular azomethine ylide 1,3-dipolar
cycloaddition reaction sequence that gives the desired tricyclic product
as a single diastereomer. A γ-amino-β-hydroxy-α-diazo
carbonyl compound is shown to fragment in the presence of a Lewis
acid to give an iminium product that can be directly reduced to the
corresponding amine.
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