Mimicking Ozonolysis via Mechanochemistry: Internal Alkynes to 1,2-Diketones using H5IO6.

Utilizing periodic acid as an environmentally benign oxidizing agent, this study introduces a novel mechanochemical method that mimics ozonolysis to convert internal alkynes into 1,2-diketones, showcasing effective emulation of ozone's reactivity. Notably, this oxidation occurs at room temperature in aerobic conditions, eliminating the need for toxic transition metals, hazardous oxidants, or expensive solvents. Through control experiments validating the mechanism, substantial evidence supports a concerted reaction pathway. This progress marks a significant stride toward cleaner and more efficient chemical synthesis, mitigating the environmental impact of conventional processes. Assessing the green chemistry metrics in both solvent-free and previously reported solvent-based methods, our eco-friendly protocol demonstrates an E-factor of 7.40, a 51.7 % atom economy, a 45.5 % atom efficiency, 100 % carbon efficiency, and 11.9 % reaction mass efficiency when solvents are not used.

Highly Regioselective Cobalt-Catalyzed Hydroboration of Internal Alkynes.

Herein, we report the development of new Co complexes that have cyclopropane-based diphosphine ligands and can catalyze highly chemo-, regio-, and stereoselective hydroboration reactions of unsymmetrical internal alkynes. These reactions exhibited unusual regioselectivity: specifically, reactions of aryl alkyl internal alkynes showed excellent cis-ß-addition selectivity, and reactions of dialkyl internal alkynes gave excellent cis-α-addition selectivity. Highly regioselective hydroboration of unsymmetrical dialkyl internal alkynes cannot be achieved by other known methods. The reactions described herein are highly synthetically useful, particularly for the stereoselective synthesis of trisubstituted alkenylborates and alkenes. Mechanistic studies indicate that a CoI -H species is a plausible active catalyst and the rigid structure of the cyclopropane skeleton of the ligands and the crowded reaction pocket were responsible for the unprecedented regioselectivity.

Silver-Catalyzed Nitration/Annulation of α-Alkynyl Arylols toward 3-Nitrated Benzofurans.

A silver-catalyzed nitration/annulation of α-alkynyl arylols is reported by using tert-butyl nitrite (TBN) as a NO2 radical precursor, from which a set of 3-nitrated benzofurans were synthesized with moderate to good yields. This transformation initiated by an in situ generated NO2 radical proceeds efficiently under mild and neutral redox conditions, which provides a new pathway toward the 3-nitrobenzofuran framework via catalytic difunctionalization of internal alkynes.

Catalytic Enantioselective Cyclopropenation of Internal Alkynes: Access to Difluoromethylated Three-Membered Carbocycles.

Herein we described an efficient RhII -catalyzed enantioselective cyclopropenation reaction of internal alkynes with a masked difluorodiazoethane reagent (PhSO2 CF2 CHN2 , Ps-DFA). This asymmetric transformation offers efficient access to a broad range of enantioenriched difluoromethylated cyclopropenes (40 examples, up to 99 % yield, 97 % ee). The synthetic utility of obtained strained carbocycles is demonstrated by subsequent stereodefined processes, including cross-couplings, hydrogenation, Diels-Alder reaction, and Pauson-Khand reaction.

Ytterbium-catalyzed formal [4+2] cycloaddition: synthesis of chalcogen-quinolines 3-unsubstituted

A regioselective ytterbium-catalyzed annulation reaction between ethylglyoxalate, anilines and silyl-alkynes bearing selenyl- and telluryl-moieties for the formation of poly-substituted quinolones is described. A series of examples formed under mild conditions are presented, including a scaled-up reaction and a study on catalyst recyclability.