Heterocycles are especially important in chemical and pharmaceutical industries. It seems that industrial people have been using mostly the traditional and conventional transformations for the synthesis of heterocycles, perhaps because those reactions are reliable and robust and proceed generally at low cost. However, it is also true that some of those reactions are accompanied with waste byproducts. In this sense, transition-metal-catalyzed reactions minimize such waste and are in general environmentally friendly. Heterocycles having a complicated structure with many labile functional groups can be synthesized often from rather simple starting materials through sequential catalytic processes.