A C–H functionalization approach to diverse nitrogenous scaffolds through conjugate addition of catalytic allyliron nucleophiles

Abstract

Cyclopentadienyliron(II) dicarbonyl complexes capable of coordinating to and enhancing the acidity of a range of unsaturated substrates have emerged as a new class of base-metal derived catalysts for C–H functionalization. In this manuscript, the iron-catalyzed C–H functionalization of allylic C(sp³)–H bonds using nitrogen containing α,β-unsaturated carbonyl compounds as coupling partners is reported. Employing a cationic cyclopentadienyliron dicarbonyl complex, this redox neutral process converts simple alkenes into allylic anion equivalents for 1,4-addition into maleimides, acyclic α,β-unsaturated imides, and vinylogous amides. The judicious pairing of pyridine and alkylamine bases with Lewis acid additives allowed each of these classes of substrates to be successfully employed, allowing for the formation of a diverse collection of cyclic and acyclic nitrogen-containing compounds featuring C–C unsaturation. The resulting Michael adducts can be further transformed into a variety of useful scaffolds such as allylated pyrroles, pyrrolidines, and carbocyclic acids.