Studies toward the total synthesis of the cytotoxic sponge alkaloid pyrinodemin A.

[structure: see text]. The syntheses of the proposed structure of pyrinodemin A (1) and its cis double bond positional isomer (C15'-C16') in racemic form are described. The key reaction involved an intramolecular nitrone/double bond cycloaddition. Our results suggest that neither 1 nor its double positional isomer is the correct structure of pyrinodemin A