Palladium-Mediated Functionalization of Benzofuran and Benzothiophene Cores

Abstract

The palladation reactions of 2-heteroaromatic primary phenethylamines bearing a benzofuran and benzothiophene nuclei have been studied. We have assessed the reactivity of the corresponding dimeric six-membered palladacycles (arising from C-H metalation) toward neutral ligands and unsaturated species. The insertion reactions of isocyanides into the Pd-C bond of the aforementioned palladacycles allowed the isolation of the corresponding iminoacyl intermediates, which could later be decomposed to give the amidine derivatives containing these relevant heterocyclic cores. In contrast, the carbonylation and alkenylation reactions led to straightforward formation of lactams and alkenylated organic derivatives. Interestingly, an unusual hydrogen-bond-promoted E-to-Z isomerization equilibrium of the resulting olefins was observed. Furthermore, we have studied the conditions to perform the alkenylation of the N-Boc derivatives of these substrates in a catalytic fashion. All the organometallic complexes (arising from the C-H activation of the heteroaromatic cores and insertion of isocyanides) and organic products (arising form the decomposition reactions) have been fully characterized, including the X-ray crystal structures of several organometallic and organic derivatives.