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

Abstract

Allylic substitution of PhCH(OAc)CHdCHPh by CH 2 (COMe) 2 in a basic MeOH/H 2 O mixture could be achieved in the absence of a palladium catalyst and lead to a mixture of PhCH(CH(COMe) 2 )CHdCHPh and PhCH(OMe)CHdCHPh 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 PdCl 2 (CH 3 CN) 2 did not accelerate the reaction but improved the selectivity, and PhCH(CH(COMe) 2 )CHdCHPh was then obtained in 92% yield while PhCH(OMe)-CHdCHPh 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 )CHdCHPh.

The application of electrospray ionization mass spectrometry to homogeneous catalysis

“…A mechanism for this transformation was proposed based on the intercepted species (Scheme 10) [65]. The role of Pd II in improving the selectivity of carbon-carbon bond formation in the allylic substitution of 1-acetoxy-1,3-diphenylpropene by acetylacetone in an aqueous system was investigated by Muzart and Roglans (Scheme 11) [15]. Scheme 11.…”

“…Since then, the primary use of ESI-MS in the area of solution-phase organometallic chemistry has been in the identification of short-lived, low concentration intermediates from catalytic mixtures. Toward this end, ESI-MS has been used to study catalytic oxidations [5][6][7][8], hydrogenations [9][10][11], hydrosilylations [12] and carbon-carbon bond-forming [13][14][15] reactions with the most attention given to palladium-catalyzed carbon-carbon bond-forming reactions [14,[16][17][18][19][20][21]. A number of book chapters have been written on the subject of ESI-MS analysis of organometallic reaction intermediates [22][23][24] and this review aims to highlight more recent advances and new directions in the field.…”

Palladium Intermediates in Solution

“…In an ongoing study using water as a solvent in palladium chemistry, Muzart et al [49,50] described the substitution of allylic acetates 51 with different nucleophiles such as acetylacetone (52) and sodium para-toluenesulfinate (54) in aqueous media using a palladium complex and the hydrophilic ligand [(HOCH 2 CH 2 NH-COCH 2 ) 2 NCH 2 ] 2 (56). Scheme 7.27 shows the specific reactions studied by ESI-MS in order to further investigate mechanistic aspects of these reactions.…”

“…Muzart et al [54] applied the analytical tool to study mechanistically the hydroxyalkoxylation of o-allylphenol 76 catalyzed by a mixture of Pd(OCOCF 3 ) 2 and the watersoluble ligand 56 (also used in the palladium-catalyzed substitution of allylic acetates in aqueous media [49,50]) with H 2 O 2 in H 2 O/MeOH to afford 2-(1,2-dihydroxypropyl)phenol derivatives 77 and 78 (Scheme 7.32). It was suggested that the reaction went through a cascade process in which, in a first step, isomerization of the double bond took place followed by epoxidaton of the olefin and the opening of the resulting oxirane (Scheme 7.32).…”

Pd-catalyzed Suzuki cross-Coupling reaction of bromostilbene: insights on the nature of the boron Species

“…Electrospray ionization mass spectrometry (ESI-MS) is a powerful tool in the identification of organometallic reaction intermediates and has been applied to the detection of intermediates in palladium-catalyzed cross coupling reactions. [15][16][17][18][19][20][21][22] However, these studies are essentially focused on the identification of palladium intermediates. Thus, we applied the ESI-MS in the negative mode to detect the boron species in the coupling reaction with (E)-bromostilbene.…”