Exploiting phosphonate chemistry in metal-mediated dearomatization: stereoselective construction of functionalized spirolactams from arene ruthenium complexes

Arene ruthenium complexes possessing beta-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 eta5-cyclohexadienyl complexes can then be diastereoselectively converted to metal-free azaspiro4.5]decane derivatives upon oxidative demetalation in the presence of suitable nucleophiles. An asymmetric spirocyclization was demonstrated through application of this procedure to a beta-amido phosphonate prepared from (S)-(-)-alpha-methyl benzylamine. The expected spirolactam product was obtained as a single enantiomer.