Gold-catalyzed annulations of allenamides

Zusammenfassung

Gold complexes have an extraordinary ability to selectively activate unsaturated carbon-carbon bonds, even in presence of more donor species, towards the addition of a nucleophile. In this context, during the last years our group has developed different types of gold(I)-catalyzed cycloadditions employing allenamides as activating substrates. In particular, in 2013 our group disclosed a partially intermolecular (2+2+2) cycloaddition between allenamides and carbonyl-tethered alkenes that allows to obtain oxa-bridged medium-sized carbocycles in a very efficient manner. Considering this precedent, we developed a fully intermolecular version of the (2+2+2) cycloaddition between allenamides, alkenes and aldehydes, that provides a direct entry to highly substituted tetrahydropyrans. Moreover, we also disclosed an enantioselective version of this method, that allow to obtain the tetrahydropyran products in an optically active manner. Finally, we demonstrated the possibility of extending this concept to the synthesis of synthetically appealing piperidines by developing an alternative gold(I)-catalyzed (2+2+2) annulation process between allenamides and alkenyl-oximes.