Total synthesis of the tricylic marine alkaloids (-)-lepadiformine, (+)-cylindricine C, and (-)-fasicularin via a common intermediate formed by formic acid-induced intramolecular conjugate azaspirocyclization

A very short and efficient enantioselective total synthesis of the tricyclic marine alkaloids (-)-lepadiformine, (+)-cylindricine C, and (-)-fasicularin is developed utilizing the formyloxy 1-azaspiro[4.5]decane as a common intermediate. The studies demonstrate that the strategy developed, represents a highly efficient method for the total synthesis of the tricyclic marine alkaloids and should be of general utility in the synthesis of these natural products.