Catalizadores de cobreclave para el acceso al esqueleto de benzo(b)furanos

Zusammenfassung

New approaches to the benzo[b]furan nucleus based on the use of copper catalysts have been developed in this research. In our first approach, 3-arylbenzofurans are prepared by an innovative protocol that involves a cascade formation of O1-C2/C2-C3 bonds. DMA is the source of C2 carbon of the furan core in a process mediated by molecular oxygen, and both the copper source and DMA can be recycled several times. The second entry to the benzo[b]furan framework implies the participation of a new non-symmetric copper pincer complex. This tailored complex is straightforwardly prepared by a short synthetic route with good overall yield, and then applied in sub-molar loadings to the heteroannulation of ortho-iodophenols and alkynes to provide 2-substituted benzo[b]furans and furo[3,2-b]pyridines. In addition, the first examples of heteroannulation from o-bromo and o-chlorophenols are reported by means of this outstandingly active copper source, which can be also applied to several C-, N-, and O-arylation reactions. Finally, as a result of an authoritative study carried out to clarify the mechanism that operates in both approaches, the role of the reagents employed, the homogeneous or heterogeneous nature of the catalytic species, some unprecedented processes (copper-catalyzed Wacker-type cyclizations, intramolecular Heck reactions, etc) and the structure of some key intermediates is revealed.