Synthesis of spiro[4.5]cyclohexadienones with an allene motif via a base-promoted intramolecular ipso-Friedel–Crafts addition of phenols to propargyl bromides
novel synthetic method for allenyl spiro[4.5]cyclohexadienone derivatives based on a base-promoted intramolecular ipso-Friedel–Crafts addition of phenols to propargyl bromides. The present spirocyclization proceeded in a CH2Cl2–tert-BuOH mixed solvent system using potassium tert-butoxide as the base, and produced the corresponding spiro[4.5]cyclohexadienone derivatives with an allene motif in up to 99%
Inspiroation: A novel synthesis of spirocycles based on a palladium‐catalyzed intramolecular ipso‐Friedel–Crafts alkylation of phenols (see scheme; dba=dibenzylideneacetone) and indoles is described. Mechanistic studies show that the reaction proceeds through an unprecedented rearomatization‐assisted oxidative addition.