Stereochemical Dichotomy in Two Competing Cascade Processes: Total Syntheses of Both Enantiomers of Spiroxin A

The first total synthesis of the marine antibiotic spiroxin A has been achieved for both enantiomeric forms. The discovery of two competing cascade processes triggered by two orthogonal stimuli, photo-irradiation or acid/base treatment, enabled the divergent conversion of a single chiral, nonracemic bis-quinone into both enantiomers of an advanced intermediate en route to both (-)- and (+)-spiroxin A. The mechanism of the enantiodivergence is discussed.