Tandem Oxidative Dearomatizing Spirocyclizations of Propargyl Guanidines and Ureas

Treatment of propargyl ureas or guanidines with iodosobenzene diacetate results in an oxidative tandem amination/etherification dearomatizing spirocyclization. This transformation leads directly to the complete framework of the <i>Leucetta</i> alkaloids, spirocalcaridine A and B.