Rc-Allylpalladium

Palladium-mediated cydization based on the reactivity of o-alkynyl or alkenyl-phenyl isonitriles have been developed [105]. On the basis of their earlier studies on the three-component synthesis of allyl aryl cyanamides [106], Yamamoto and co-workers reported a palladium-catalyzed three-component coupling reaction of 2-alkynylisocyanobenzenes 122 with allyl methyl carbonate and trimethylsilylazide leading to N-cyanoindoles 125 [107]. One of the key steps of the proposed mechanism is the formation of 7i-allylpalladium carbodiimide 123 and its isomerization to rc-allylpalladium cyanamide complex 124 (Scheme 8.50). 

The construction of the 2,3-dihydrofuran moieties of breviones was reported in which the epoxide and the a-pyrone depicted in the following scheme underwent both C-alkylation and consecutive O-alkylation presumably via rc-allylpalladium complexes <02TL1713>. 

If nucleophilic attack constitutes the stereoselective step, special substitution patterns of the intermediate rc-allylpalladium complex are suitable for enantioselective catalysis, Racemic substrates with identical substituents in positions 1 and 3 give rise to chiral complexes incorporating a meso-n- y ligand. In this case, enantioselectivity is determined by discrimination of the nucleophile for the diastereotopic termini of the allylic system. 

Scheme 11.10 Stereocontrolled acetate attack on rc-allylpalladium complexes.

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