A new route to spiropyrrolidinyl-oxindole alkaloids via iodide ion induced rearrangement of [(N-aziridinomethylthio)methylene]-2-oxindoles.

A new approach for the synthesis of spiropyrrolidinyloxindole alkaloids, i.e. coerulescine (4) and horsfiline (5) has been developed via iodide ion induced rearrangement of [(N-aziridinomethylthio)methylene]oxindoles 2 to the respective spiropyrroline-2-oxindole derivatives 3 and their subsequent one-pot reductive dethiomethylation-N-methylation. [reaction: see text]