Synthesis of Spirocyclic or Fused Cyclic Compounds Using Transition Metal-Catalyzed Dearomatization of Phenols

This review describes the development of novel dearomatization reactions of phenols using transition metal catalysis. We found that an intramolecular ipso-Friedel-Crafts allylic alkylation of phenols proceeded smoothly in the presence of Pd catalyst, producing various spiro[4.5]cyclohexadienone derivatives. The present methods could be applied to a catalytic asymmetric reaction. An asymmetric intramolecular Friedel-Crafts allylic alkylation of phenols to produce chiral 10-vinyl 9,10-dihydrophenanthrenes was also investigated. The developed process was successfully applied to the enantioselective synthesis of bioactive natural products. We also developed a novel method for synthesizing spirocycles based on a Pd-catalyzed intramolecular ipso-Friedel-Crafts alkylation of phenols to η3-propargylpalladium(II) complexes. Mechanistic studies revealed that the present reaction proceeds through a rearomatization-assisited oxidative addition. An Au-catalyzed carbocyclization of phenols with a terminal alkyne via an intramolecular ipso-Friedel-Crafts alkenylation is also discussed.