An iodoazide radical cascade cyclization strategy has been used as the key step in a formal synthesis of aspidospermidine. Specifically, this step generated the alkaloid's B- and E-rings in the ethylidene-functionalized tetracycle 5. In turn, this was converted into pentacycle 25, a known advanced synthetic precursor of aspidospermidine.
A new stereoselective approach to the tetracyclic core of Aspidosperma alkaloids is described.
Selective attack by tristrimethylsilylsilyl radicals on the aryl carbon−iodine bond of iodoaryl azides
was first demonstrated on the simple model 15, thus both extending the recent discoveries of Kim
and co-workers on aliphatic C−I bonds and demonstrating that the selectivity can be exploited in
cascade radical cyclizations. Extension to the more complex substrate 25 afforded the core ABCE
tetracyclic skeleton of the alkaloids in excellent yield and with efficient control of relative
stereochemistry.
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