Cascade Synthesis of Pyrroles from Nitroarenes with Benign Reductants Using a Heterogeneous Cobalt Catalyst

Abstract

Ab ifunctional 3d-metal catalyst for the cascade synthesis of diverse pyrroles from nitroarenes is presented. The optimal catalytic system Co/NGr-C@SiO 2-L is obtained by pyrolysis of ac obalt-impregnated composite followed by subsequent selective leaching.I nt he presence of this material, (transfer) hydrogenation of easily available nitroarenes and subsequent Paal-Knorr/Clauson-Kass condensation provides > 40 pyrroles in good to high yields using dihydrogen, formic acid, or aC O/H 2 Om ixture (WGSR conditions) as reductant. In addition to the favorable step economy,this straightforward domino process does not require any solvents or external cocatalysts.The general synthetic utility of this methodology was demonstrated on avariety of functionalizedsubstrates including the preparation of biologically active and pharmaceutically relevant compounds,for example,(+ +)-Isamoltane.

Iodine‐Modified Pd Catalysts Promote the Bifunctional Catalytic Synthesis of 2,5‐Hexanedione from C6 Furan Aldehydes

“…[17][18][19] Among these compounds, 2,5-hexanedione (HD) is an important high-value commodity chemical for performing various upgrades to solvents, polymers, fragrances, and drugs. [20][21][22][23][24] The hydrogenative ring-opening of 5-methylfurfural (MF) to HD has been widely reported over combinations of metals and acids (such as Au/TiO 2 , Pd/Nb 2 O 5 , Ni 2 P/mordenite, Ni 2 P + HZSM-5) under a water solvent by successive C=O hydrogenation, ring-opening, and C=C hydrogenation. [19,[25][26][27] The reaction suffers a high reaction temperature of 130-250 °C.…”

“…To decrease the carbon footprint and develop a sustainable economy, these catalysts have attracted widespread interest for use in the upgrading of unsaturated biomass‐derived C 6 furfurals (5‐methylfurfural, 5‐hydroxymethylfurfural) to valuable chemicals, such as hydrogenative etherification to furan ethers (2‐alkoxymethyl‐5‐methylfuran, 2,5‐bisalkoxymethylfuran), [5–7] hydrogenative ring‐rearrangement to cyclic ketones (3‐methylcyclopentanone, 3‐hydroxymethylcyclopentanone), [8–13] hydrogenative hydrogenolysis to 2,5‐dimethylfuran and 2,5‐dimethyl tetrahydrofuran, [14–16] hydrogenative ring‐opening to linear ketones (1‐hydroxyl‐2,5‐hexanedione, 2,5‐hexanedione) [17–19] . Among these compounds, 2,5‐hexanedione (HD) is an important high‐value commodity chemical for performing various upgrades to solvents, polymers, fragrances, and drugs [20–24] …”