Transition-Metal-Free, Atom- and Step-Economic Synthesis of Aminoketopyrrolizines from Benzylamine, Acylethynylpyrroles, and Acylacetylenes

A concise, atom-economic strategy for the synthesis of pyrrolizines with amino and keto substituents has been developed. It includes the following key steps: (i) the base-catalyzed (K₃PO₄/DMSO) addition of a benzylamine to 2-acylethynylpyrroles and (ii) noncatalyzed addition of enaminones obtained to the triple bond of acylacetylenes followed by intramolecular cyclization of the intermediate pentadiendiones thus formed to the target 1-(benzylamino)-2-acyl-3-methylenoacylpyrrolizines