Multicomponent reactions studies: Yonemitsu-type trimolecular condensations promoted by Ti(IV) derivatives

We have developed a Ti(IV)/Et3N-promoted trimolecular condensation of aromatic heterocycles (furan, pyrrole, imidazole, indole) with aldehydes and active methylene compounds. In the case of indole and methyl acetoacetate the reaction afforded three-component products or tricyclic cyclopenta[b]indole derivative, depending on the reaction conditions. In both cases, NMR analysis evidenced that titanium enolate is the reactive species involved in the reaction.