Heterocyclic Spiranes and Dispiranes via Enantioselective Phosphine-Catalyzed [3+2]?Annulations

The synthesis of highly functionalized heterocyclic spiranes has been carried out by [3+2] cyclizations between allenoates and enones, under phosphine catalysis. Excellent enantioselectivity levels (ees up to 99%) have been attained in FerroPHANE-promoted cyclizations of this class, leading to chiral sulfides with unprecedented spiranic structures. The corresponding sulfoxides have been obtained then via a subsequent, highly diastereoselective oxidation of the prostereogenic sulfur centre.