Assembly of a Key Dienic Intermediate for Tetrodotoxin via a Machetti–DeSarlo Reaction

A route to a racemic diene intermediate for the synthesis of tetrodotoxin is described. Key steps of the sequence leading to such a compound include the oxidative amidation of a phenol, a Cu­(II)-catalyzed cyclocondensation of a nitroketone with an olefin (Machetti–DeSarlo reaction), and a nucleophilic fragmentation of the resulting isoxazoline. Several unusual reactions encountered in the course of this study are thoroughly discussed