Microwave-assisted cerium(III)-promoted cyclization of propargyl amides to polysubstituted oxazole derivatives

Article abstract of DOI:10.1002/ejoc.201101302

Functionalized polysubstituted oxazoles are an important class of five-membered N,O-heterocycles that occur widely in the structure of natural products and fine chemicals. They are also often used as building blocks in the synthesis ofheterocyclic molecules with more complex structures. Therefore, efficient synthetic protocols based on Lewis acid promoted reactions are desirable. In this context, we report that, under microwave irradiation, the CeCl₃·7H₂O/NaI/I₂ system is capable of promoting a 5-exo-dig cyclization of propargyl amides with good functional group tolerance. The microwave reactor also provides a more convenient and safer method for heating the reaction. This methodology represents a straightforward CeCl₃·7H₂O/NaI/I₂ promoted cyclization using microwave irradiation to accomplish the synthesis of polysubstituted oxazole derivatives. After a wide-ranging scientific investigation on the use of cerium(III) salts as promoters for useful organic transformations, we describe here a new, microwave-assisted reaction involving the combinationof CeCl ₃·7H₂O/NaI/I₂ for the construction of N,O-heterocycles. The study concerns the preparation of highly substituted oxazoles starting from N-propargyl carboxamides. Copyright