Novel Method for Synthesizing Spiro[4.5]cyclohexadienones through a Pd-Catalyzed Intramolecular <i>ipso</i>-Friedel−Crafts Allylic Alkylation of Phenols
The first successful Pd-catalyzed intramolecular ipso-Friedel−Crafts allylic alkylation of phenols, which provided a new access to spiro[4.5]cyclohexadienones, is described. The present method could be applied to catalytic enantioselective construction of an all-carbon quaternary spirocenter.
Enantioselective construction of all-carbon quaternary spirocenters through a Pd-catalyzed asymmetric intramolecular ipso-Friedel–Crafts allylic alkylation of phenols
A novel catalytic asymmetric synthetic method for making spirocyclohexadienones with an all-carbon quaternary spirocenter was developed based on the Pd-catalyzed intramolecular ipso-Friedel-Crafts allylic alkylation of phenols. When 5 mol % of the Pd catalyst and 12 mol % of (-)-9-NapBN (-)-3e were used, the spirocyclic adduct was obtained with up to 93% ee, albeit with low chemical yield. On the other hand, when using 6 mol% of the Trost ligand (R,R)-3k, the spirocyclic adducts were obtained in good yields with up to 89% ee (diastereoselectivity = 9.2:1). (c) 2012 Elsevier Ltd. All rights reserved.