Iron-catalyzed synthesis of heterocycles

Some PdI 2 -based complexes have proved to be efficient catalysts for the selective, atom-economical synthesis of different important heterocyclic derivatives starting from very simple building blocks, such as simple or functionalized alkynes, amino alcohols, diamines, carbon monoxide, carbon dioxide, alcohols, water, and oxygen. The synthetic protocols leading to heterocycles have been grouped into three classes of reactions: (a) cycloisomerization of (Z)-2-en-4-yn-1-ols, (Z)-2-en-4-yne-1-thiols, (Z)-(2-en-4-ynyl)amines, 2-alkynylbenzyl alcohols to give substituted furans, thiophenes, pyrroles, and 1,3-dihydroisobenzofurans or 1H-iso-chromenes, respectively; (b) oxidative carbonylation of simple alkynes, 1,5-diynes, functionalized alkynes bearing a suitably placed nucleophilic group, amino alcohols, and diamines to afford substituted maleic anhydrides, functionalized p- and γ-lactones, β- and γ-lactams, dihydroindol-2-ones, furans, pyrroles, thiophenes, tetrahydrofurans, oxazolidin-2-ones, oxazolines, cyclic ureas, 4H-3,1-benzoxazines, quinazolin-2-ones, quinolin-4-ones; (c) reductive carbonylation of alkynes to give substituted γ-lactones and formation of lactone or anhydride derivatives by additive carbonylation, resulting from the combination between oxidative carbonylation of the triple bond and reduction of a suitable functional group present in the substrate itself.