Reactions Involving Oxidative Addition of Allylic Electrophiles

Reactions Involving Oxidative Addition of Allylic Electrophiles 

One of the most common methods employed for the generation of allylpalladium complexes involves oxidative addition of allylic electrophiles to Pd . This transformation has been explored by several groups, and has been the topic of recent reviews [69]. A representative example of this process was demonstrated in a recent total synthesis of (+ )-Biotin [70]. The key step in the synthesis was an intramolecular amination of 89, which provided bicydic urea derivative 90 in 77% yield (Eq. (1.40)). In contrast to the Pd -catalyzed reactions of allylic acetates bearing pendant amines described above (Eq. (1.10)), which proceed via alkene aminopalladation, Pd -catalyzed reactions of these substrates occur via initial oxidative addition of the allylic acetate to provide an intermediate Jt-allylpalladium complex (e.g., 91). This intermediate is then captured by the pendant nudeophile (e.g., 91 to 90) in a formal reductive elimination process to generate the product and regenerate the Pd catalyst. Both the oxidative addition and the reductive elimination steps occur with inversion 

A number of studies have focused on the development and application of asymmetric versions of Pd-catalyzed allyUc alkylation reactions [72]. Trost has developed a class of ligands, including 94 and 9S, that provide excellent yields and enantioselectivities for many of these reactions. For example, treatment of aUylic acetate 92 with 1 mol% of allylpalladium chloride and 3 mol% of ligand 94 led to the formation of 93 in 97% yield and 91% ee (Eq. (1.41)) [73]. Asymmetric desymme-trization reactions of meso-bis-carbamates that provide heterocyclic products have also been described [74]. 

Recently, Trost has employed this methodology in a tandem one-pot ene-yne couphng/enantioselective aUylation process [75]. This transformation was used for the construction of pyrrohdine 99, an intermediate in a formal synthesis ofkainic add [75b]. As shown below (Eq. (1.42)), ruthenium-catalyzed coupling of 96 with 97 provided intermediate allyl ether 98. Addition of 2 raol% of allylpalladium chloride 

Related reactions of vinylaziridines [79] or activated vinylcyclopropanes [80] with isocyanates and other heterocumulenes have been developed for the construction of cyclic ureas and similar heterocydes. For example, Trost has recently described a dynamic kinetic asymmetric reaction of aziridine 105 with phenylisocyanate that 

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