Allylic Substitution Mediated by Water and Palladium: Unusual Role of a Palladium(II) Catalyst and ESI-MS Analysis

Abstract

Allylic substitution of PhCH(OAc)CHCHPh by CH2(COMe)2 in a basic MeOH/H2O mixture could be achieved in the absence of a palladium catalyst and lead to a mixture of PhCH(CH(COMe)2)CHCHPh and PhCH(OMe)CHCHPh in 40% and 55% yields, respectively. The process is induced by water, and nucleophilic attack addition occurred on a stabilized carbocation as the intermediate. Addition of a catalytic amount of PdCl2(CH3CN)2 did not accelerate the reaction but improved the selectivity, and PhCH(CH(COMe)2)CHCHPh was then obtained in 92% yield while PhCH(OMe)CHCHPh was observed in trace amounts. An ESI-MS analysis of the reaction mixture led us to assume that a palladium acetylacetonate complex is involved in the formation of PhCH(CH(COMe)2)CHCHPh.