2,3-Dichloropyridine N-oxide, a novel oxygen transfer reagent, allows the conductance of the gold­(I)-catalyzed oxidation of alkynes to 1,2-dicarbonyls in the absence of any acid additives and under mild conditions to furnish the target species, including those derivatized by highly acid-sensitive groups. The developed strategy is effective for a wide range of alkyne substrates such as terminal- and internal alkynes, ynamides, alkynyl ethers/thioethers, and even unsubstituted acetylene (40 examples; yields up to 99%). The oxidation was successfully integrated into the trapping of reactive dicarbonyls by one-pot heterocyclization and into the synthesis of six-membered azaheterocycles. This synthetic acid-free route was also successfully applied for the total synthesis of a natural 1,2-diketone.

Internal alkynes have been shown to undergo oxidation to substituted benzils (1,2‐diarylethane‐1,2‐diones) by α‐picoline N‐oxide in the presence of Ph3PAuNТf2 (5 mol‐%). In addition to the unsubstituted benzil, the method allows preparing, under markedly mild conditions (50 °C in chlorobenzene), various non‐symmetrical products, including heteroaromatic versions thereof which are much more difficult to obtain otherwise. This gold(I)‐catalyzed transformation was integrated into one‐pot reaction sequence delivering a range of 5‐ to 7‐membered ring systems (imidazoles, quinoxalines, 1,2,4‐triazines, pyrazines, and 1,4‐diazepines), thus linking these important heterocyclic motifs to the internal alkyne reagent space.

Three‐component [2+2+1] gold(I)‐catalyzed reaction of internal alkynes (alkynyl esters or ‐ketones), nitriles, and 2‐chloropyridine N‐oxide led to a wide range of fully substituted 1,3‐oxazoles (32 examples; up to 92% isolated yields). Nitrile R3CN species, employed in the reaction as both reactants and solvents, comprise conventional nitriles (R3=Alk, Ar) and also push‐pull systems such as cyanamides (R3=NH2 and NAlk2) and the thiocyanate (R3=SPr). The advantages of the developed method include mild reaction conditions, high functional‐group tolerance, broad range of substituents R1/R3 along with a possibility of easy modification of COR2 or the amino group when R1=NH2.magnified image

By performing combined XRD and theoretical studies, we established the modes of REWGI⋯I–Pt XBs with [Pt2(μ-I)2I4]2− acting as an XB acceptor.

Efficient gold(I)-catalyzed oxidation of COR 2 -functionalized internal alkynes to vicinal tricarbonyl compounds by 2,6-dichloropyridine N-oxide proceeds under mild conditions (DCM, rt). This catalytic reaction provides a good to excellent yielding route to diverse tricarbonyls such as α,β-diketoesters, 1,2,3-triketones, and α,β-diketoamides. The utility of these compounds was also demonstrated by facile one-pot synthesis of important azaheterocyclic systems.