Development of an Organoautocatalyzed Double σ-Bond C(sp2)-N Transamination Metathesis Reaction

Abstract

The transamination reaction, which involves the conversion of one amine to another, traditionally relies on biological enzyme catalysts. Although chemists have recently developed a few transition metal-catalyzed methods, mimicking these enzymes to interconvert amine groups in acyclic substrates via transamination metathesis of a single C(sp²)─N bond, transamination of cyclic tertiary amines has remained a challenge in synthetic chemistry. Here, we present the development of organoautocatalyzed transamination metathesis of two C(sp²)─N bonds in a cyclic substrate that allows for the challenging transformation to take place with up to 95% yield under exceptionally mild reaction conditions at room temperature without external catalysts and/or additives. The reaction mechanism has been studied in detail through time-resolved ¹H-NMR, 2D NMR, and computational methods. Remarkably, in situ-formed pyrrolidinium salt acts as a hydrogen bond donor (HBD) organoautocatalyst in this multi-step domino process. The new organoautocatalyzed methodology gives environmentally friendly, atom-economical, straightforward, and rapid access to N-substituted 3,5-dinitro-1,4-dihydropyridines (DNDHPs), thus offering facile entry to privileged bioactive compounds.