Cyclopalladation heterocyclic synthesis

Herein, we review nonexhaustively our contribution to the field of transition-metal-mediated heterocyclic synthesis. This chemistry is based mainly on using cyclopalladated complexes and their reactions with disubstituted alkynes that in many cases, lead to heterocyclic products by the selective intramolecular formation of carbon-carbon and carbon-heteroatom (C-N, C-O and C-S) bonds. In some instances these reactions also lead to interesting carbocyclic derivatives. Emphasis is placed on the transformations of the alkynes. When they are allowed to react with the metallated ligands, they lead in several instances to heterocyclic or carbocyclic final products. We present in particular some of the more recent results emanating from our laboratory and comment briefly on some similarities of this chemistry to other, selected and related transition-metal-mediated reactions, thus demonstrating that this field of research remains in vogue in many different research groups. 

In most of the heterocyclizations seen previously, alkynes are used as C-2 units linking the o-bonded carbon atom and the nitrogen atom of the cyclopalladated starting materials. Dienes also play a similar role leading to a broader scope for heterocyclic synthesis. 

Scheme 2.15 Heterocycle synthesis via four-membered-ring cyclopalladation complex.

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