Synthesis of Heterocycles via Palladium-Catalyzed Carbonylations

The major developments of palladium-catalyzed carbonylative syntheses of heterocycles was reviewed. The application of palladium catalyzed carbonylation reactions in the synthesis of four membered lactones was first reported by Cowell and Stille in 1980. They used PdCl2(PPh3) 2 as catalyst, and the lactones were synthesized in high yields under mild conditions. Dupont and co-workers developed a Pd(OAc)2/2- PyPPh2 system for the production of various lactones from alkynols. Palladium catalyzed carbonylation of aziridines represents another convincing procedure for the synthesis of lactams. The methodologies developed by Brickner and Tsuji and their co-workers successfully avoid the use of aziridines in the preparation of lactams, but the specificity of starting materials limited the scope. Six-membered ring lactones were produced preferentially in acetonitrile using cationic palladium complexes coordinated by certain chelating diphosphines (dppb) as catalyst.