Cyclopalladated complexes vinyl substitutions

Stable, cyclopalladated complexes sometimes may be used in vinyl substitution but these reactions cannot be carried out catalytically. A major limitation is that few cyclopalladated structures are available and only a few types of vinyl substitution products can be made by this procedure. 

Vinyl substitutions with N,N-dialkylbenzylamine-cyclopalladated complexes have been studied most thoroughly. In the presence of triethylamine the substitution occurs quite selectively with styrene derivatives19 and a,p-unsaturated carbonyl compounds.20 For example, chloride-bridged cyclopalladated NJ4-dimethylbenzylamine dimer and methyl vinyl ketone give 92% of o-dimethylaminomethylbenzalacetone in 1 h at 110 C (equation 6). 

These alkenylation products are easily utilized for the formation of heterocyclic compounds by cyclization reactions. For example, ethyl A -methyl-lV-(3,4-methylenedioxy)benzylglycinate is cyclopalladated regiospecifically at C(6) when treated with Li2PdCl4. The product, the di-p-chloro-bis(AOV-dialkylbenzylamine-6-C,iV)-dipalladium(II) complex 7.19, undergoes a substitution reaction via the insertion of methyl vinyl ketone between the palladium metal and the phenyl carbon atom. The resultant p-aryl-a,p-unsaturated ketone 7.20 is cyclized using anhydrous potassium carbonate in ethanol to the corresponding ethyl iV-methyl-1,2,3,4-tetrahydroisoquinolinium-3-carboxylate 7.21, as shown in Eq. (7.19) [76, 77]. 

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