A biogenetically inspired heterodimerization approach to the synthesis of the core structure of the alkaloid fissoldhimine

A biogenetically inspired heterodimerization reaction of N-substituted 2-pyrroline equivalents leads to the tricyclic core of the alkaloid fissoldhimine. Thus, pyrrolidin-2-ol derivatives, in which the nitrogen atom is substituted either with urea or thiourea functionality, serve as equivalents of the corresponding N-substituted 2-pyrrolines. Reaction of these compounds under Lewis acidic (e.g., lanthanide triflate) or Brønsted acid conditions leads to a diastereomeric form of the tricyclic core of fissoldhimine. The reaction can be envisaged to occur either via an asynchronous intermolecular inverse electron demand hetero-Diels-Alder reaction, or through a tandem Mannich/ring-closure reaction.