Regioselective additions to P -allyl metal complexes
Highly regioselective additions to allylic acetates, catalyzed by palladium (0), can be achieved by incorporation of a thioether or tertiary amine on the substrate. Reactions with malonate anion are highly selective for the terminus of the allyl moiety proximal to the heteroatom. Palladium catalyzed allylations of stabilized nucleophiles is a well-established procedure which has been shown to be of great synthetic utility.1,2>3 Substitutions of 1- or 3-substituted allylic acetates tend to be selective for the less substituted terminus (Scheme 1).2 Reactions of 1,3-disubstituted allylic acetates can lead to a mixture of regioisomeric substitution products. The problems associated with substitution selectivity have been partially addressed in several ways. Polarizing functional groups such as carbony44 a~etate,~ alkoxide,6 or alcohol7 adjacent to the rr-ally1 complex promote addition distal to that group. Steric hindrance at one terminus of allyl moiety can direct the substitution away from that In addition, enhanced control over the position of substitution has been achieved by the use of catalysts bearing sterically hindered bidentate ligands.10,ll In spite of these efforts the problem has not been completely solved.