Palladium-Catalyzed Reactions Of Enynols And Nucleophiles For The Synthesis Of Cyclopentadienes And Pyrrole Derivatives

Palladium-catalyzed cyclizations of enynes provide a highly atom-economical method for the synthesis of carbo-and heterocycles under mild conditions. A large amount of Pd-catalyzed tandem cyclizations of enynes and nucleophiles for the cyclizations were reported in recent years, aimed at further extending the level of functionalization of products. This work was focused on the synthesis of cyclopentadienes and pyrrole derivatives by using Pd-catalyzed reaction or addition reaction. The results are presented in three parts as follows.The first part introduces a brief review of Pd-catalyzed enyne cycloisomerizations. It outlines the background, reaction mechanism, and organic synthesis applications of Pd-catalyzed enyne cyclizations in organic synthesis. The reaction mechanism would proceed by either enyne rearrangement or enyne tandem reaction, depending on the substrates. In particular, Pd-catalyzed reactions of enynes and nucleophiles involved are described in more detail.The second part develops the synthesis of tetrasubstituted cyclopentadienes via Pd-catalyzed reactions of (Z)-2-en-4-yn acetates and N-Methyl indoles. It is suggested that the cyclopentadiene formation undergoes a reaction sequence which includes Fridel-Crafts arylation,1,5indole migaration, Nazarov electrocyclization, and1,2indole migration. The method offers advantages like mild conditions, simple performance, and wide applicability. Furthermore, this cyclization reaction succeeded in applying to other nucleophiles, giving halogen substituted cyclopentadienes.The third part involves the synthesis of (E)-3-styryl-2,5-dihydro-1H-pyrrole derivatives via Pd-catalyzed nucleophulic addition of indoles to hydroxy1,6-enynes. The reaction was carried out under mild conditions, by which1,6-enynes were selectively transformed into (E)-3-styryl-2,5-dihydro-1H-pyrrole derivatives. The reaction proceeded with some other substituted enynes and indoles in yields ranging from27to74%.