Palladium-Catalyzed Allylic Substitution with (η6-Arene-CH2Z)Cr(CO)3-Based Nucleophiles

Although the palladium-catalyzed Tsuji-Trost allylic substitution reaction has been intensively studied, there is a lack of general methods to employ simple benzylic nucleophiles. Such a method would facilitate access to alpha-2-propenyl benzyl motifs, which are common structural motifs in bioactive compounds and natural products. We report herein the palladium-catalyzed allyiation reaction of toluene-derived pronucleophiles activated by tricarbonylchromium. A variety of cyclic and acyclic allylic electrophiles can be employed with in situ generated (eta(6)-C6H5CHLiR)Cr(CO)(3) nucleophiles. Catalyst identification was performed by high throughput experimentation (HTE) and led to the Xantphos/palladium hit, which proved to be a general catalyst for this class of reactions. In addition to eta(6)-toluene complexes, benzyl amine and ether derivatives (eta(6)-C(6)H(5)CH(2)Z)Cr(CO)(3) (Z = NR2, OR) are also viable pronucleophiles, allowing C-C bond-formation alpha to heteroatoms with excellent yields. Finally, a tandem allylic substitution/demetalation procedure is described that affords the corresponding metal-free allylic substitution products. This method will be a valuable complement to the existing arsenal of nucleophiles with applications in allylic substitution reactions.