Palladium TPPTS catalyst in water: C-allylation of phenol and guaiacol with allyl alcohol and novel isomerisation of allyl ethers of phenol and guaiacol

Abstract

The use of allylic alcohols for the direct synthesis of alkenylphenols instead of allylic halides is highly attractive. However, such phenol allylations mainly lead to the production of phenyl ethers (O-allylation). We introduce herein the potential of palladium TPPTS complexes in water for a selective C-allylation of phenol and guaiacol by allyl alcohol into allylphenols and eugenols (0.8 < para/ ortho < 2). With the same reaction conditions, in presence of an excess of phenol in basic conditions, allyl phenyl ether is isomerised into C-allylated compounds through a catalytic allyl transfer from the allyl ether to the phenate which is present in excess in the aqueous phase. A similar isomerisation reaction occurs with allyl guaiacyl ether. Intermolecular allyl transfers between allyl phenyl ether and guaiacol or between allyl guaiacyl ether and phenol were observed and also led to the production of C-allylated compounds. All these catalytic reactions are based on the well characterized cationic complex [π-allylpalladium(TPPTS) 2] + generated through the facile heterolytic cleavage of allyl alcohol or allyl phenyl ether by the Pd(0) TPPTS complex. This π-allylpalladium(II) TPPTS complex is stable in water at room temperature.