Exploiting Phosphonate Chemistry in Metal-Mediated Dearomatization:  Stereoselective Construction of Functionalized Spirolactams from Arene Ruthenium Complexes

Arene ruthenium complexes possessing β-amido phosphonate side chains participate in intramolecular spirocyclization reactions to deliver stable cyclohexadienyl ruthenium adducts. Spirocyclization is accomplished via a tandem two-step sequence that involves stereoselective nucleophilic aromatic addition to the ipso position of the coordinated arene, followed by intermolecular Horner−Wadsworth−Emmons olefination. The resulting η5-cyclohexadienyl complexes can then be diastereoselectively converted to metal-free azaspiro[4.5]decane derivatives upon oxidative demetalation in the presence of suitable nucleophiles. An asymmetric spirocyclization was demonstrated through application of this procedure to a β-amido phosphonate prepared from (S)-(−)-α-methyl benzylamine. The expected spirolactam product was obtained as a single enantiomer.