A New Microwave-Assisted Catalytic Domino Process for the Synthesis of N-Heterocycles

摘要

Several N-heterocycles including 3,4-dihydro-2H-1,4-benzoxazines, 1,2,3,4-tetrahydroquinoxalines, 1,2,3,4-tetrahydroquinolines and 3,4-dihydro-2H-1,4-benzothiazines can easily be obtained from ω-nitroalkenes via a new domino reaction under the influence of microwave irradiation in a single step. Due to their biological activity the development of new methods for the synthesis of N-heterocycles is a central theme of research in organic synthesis. Reductive cyclizations of nitro compounds have been used predominantly to synthesize indoles and related N-heteroaromatics. The best known methods include the preparation of indoles according to Leimgruber-Batcho, Bartoli and Reissert, the transition metal catalyzed reductive N-heteroannulation of o-nitrostyrenes and the Cadogan cyclization. Still little is known about the application of reductive cyclizations to the synthesis of saturated N-heterocycles. In addition, the potential of the nitroso ene reaction for the formation of C-N bonds has by no means been exhausted. In particular, efficient methods for the generation of the nitroso group from easily accessible precursors in a single step are lacking. Furthermore, the primary product of the nitroso ene reaction is a hydroxyl amine instead of the much more interesting amine.