Hydroamination of alkynes as a new source of Imines for Ugi MCRs - Scope and Limitations

The hydroamination of alkynes has been implemented to form imines which are involved in Ugi multicomponent reactions. The catalytic hydroamination (using Zn(OTf)2, clays and Au catalysts) of anilines with terminal alkynes has furnished the corresponding imines with useful yields and these intermediates have been reacted in a tandem manner with isocyanides and carboxylic acids to yield the Ugi adducts. Although synthetically useful, as the process enables the use of alkynes as inputs in Ugi reactions, the main limitation deals with the low overall yields and the incompatibility of isocyanides with the metal catalysts which prevents the direct interaction of all four components. However, a one-pot process, separating both reactions, is feasible.