Selective Reductive Coupling of Vinyl Azaarenes and Alkynes via Photoredox Cobalt Dual Catalysis.

A visible light-induced Co-catalyzed highly regio- and stereoselective reductive coupling of vinyl azaarenes and alkynes has been developed. Notably, Hünig's base together with simple ethanol has been successfully applied as the hydrogen sources instead of commonly used Hantzsch esters in this catalytic photoredox reaction. This approach has considerable advantages for the straightforward synthesis of stereodefined multiple substituted alkenes bearing an azaarene motif, such as excellent regioselectivity (>20 : 1 for >30 examples) and stereoselectivity (>20 : 1 E/Z), broad substrate scope and good functional group compatibility under mild reaction conditions, which has been utilized in the concise synthesis of natural product monomorine I. A reasonable catalytic reaction pathway involving protolysis of the cobaltacyclopentene intermediate has been proposed based on the mechanistic studies.

Pd-catalyzed amidation of 1,3-diketones with CO and azides via a nitrene intermediate.

An efficient Pd-catalyzed amidation of 1,3-diketones has been developed using carbon monoxide and organic azides. This reaction provides a step-economic approach to produce ß-ketoamides from readily available compounds under mild ligand-, oxidant-, and base-free conditions. The mechanistic studies showed that the reaction occurred through an in situ generated isocyanate intermediate.

Intermolecular C-H Amidation of (Hetero)arenes to Produce Amides through Rhodium-Catalyzed Carbonylation of Nitrene Intermediates.

Amide bond formation is one of the most important reactions in organic chemistry because of the widespread presence of amides in pharmaceuticals and biologically active compounds. Existing methods for amides synthesis are reaching their inherent limits. Described herein is a novel rhodium-catalyzed three-component reaction to synthesize amides from organic azides, carbon monoxide, and (hetero)arenes via nitrene-intermediates and direct C-H functionalization. Notably, the reaction proceeds in an intermolecular fashion with N2 as the only by-product, and either directing groups nor additives are required. The computational and mechanistic studies show that the amides are formed via a key Rh-nitrene intermediate.

Co(II)/Ag(I) Synergistically Catalyzed Monoinsertion Reaction of Isocyanide to Terminal Alkynes with H2O: Synthesis of Alkynamide Derivatives.

A Co(II)/Ag(I) synergistically catalyzed three-component reaction of isocyanide with terminal alkyne and water to afford alkynamide derivatives is reported. The insertion of monoisocyanide into the C-H bond of terminal alkynes is an efficient, straightforward, atom-economical route to alkynamides, which are useful synthons in organic synthesis. This synergistic process achieves the cleavage of a C-H bond and the construction of new C-C and C═O bonds under mild conditions through the reaction of Co(II)-activated isocyanides and a Ag(I)-complex-activated terminal alkyne. This reaction has broad substrate versatility and functional group tolerance.

Co-Catalyzed Synthesis of N-Sulfonylcarboxamides from Carboxylic Acids and Sulfonyl Azides.

A Co-catalyzed effective synthesis of N-sulfonylcarboxamides from the reaction of carboxylic acids and organic azides in the presence of isocyanide has been developed. The protocol has the advantages of short time, low temperature, and being oxidant-free, which provides a new and simple approach for the synthesis of N-sulfonylcarboxamides in good to excellent yields with a broad substrate scope.

Cobalt(ii)-catalyzed bis-isocyanide insertion reactions with sulfonyl azides via nitrene radicals: chemoselective synthesis of sulfonylamidyl amide and 3-imine indole derivatives.

A chemoselective Co(ii)-catalyzed effective synthesis of sulfonylamidyl amide and 3-imine indole derivatives by using isocyanides and sulfonyl azides has been developed. This protocol provides a new, environmentally friendly and simple strategy for the efficient synthesis of the sulfonylamidyl amide and 3-imine indole derivatives with a wide range of substrates in the absence of any oxidants and additives.

Cobalt(II)-Catalyzed Isocyanide Insertion Reaction with Sulfonyl Azides in Alcohols: Synthesis of Sulfonyl Isoureas.

A Co(II)-catalyzed isocyanide insertion reaction with sulfonyl azides in alcohols to form sulfonyl isoureas via nitrene intermediate has been developed. This protocol provides a new, environmentally friendly, and simple strategy for the synthesis of sulfonyl isourea derivatives by employing a range of substrates under mild conditions.

Cobalt-Catalyzed Annulation of Amides with Isocyanides via C(sp2)-H Activation.

A cobalt-catalyzed [4 + 1] cycloaddition of easily accessible amides with isocyanides for the efficient synthesis of 3-iminoisoindolinone derivatives in high yield under mild conditions via intramolecular C(sp2)-H activation and isocyanide insertion is reported. The annulation was found to be applicable to a broad range of substrates, including arylamides, heteroarylamides, and acrylamide derivatives. Strongly coordinating N-heterocyclic directing groups such as pyridine, pyrimidine, and even pyrazole were fully tolerated in this cobalt-catalyzed C-H activation reaction.

Pd-Catalyzed Intramolecular Heck Reaction, C(sp(2))-H Activation, 1,4-Pd Migration, and Aminopalladation: Chemoselective Synthesis of Dihydroindeno[1,2,3-kl]acridines and 3-Arylindoles.

Palladium-catalyzed intramolecular Heck reaction and aminopalladation of N-(2-(1-phenylvinyl)phenyl)aniline for the efficient synthesis of dihydroindeno[1,2,3-kl]acridines and 3-arylindoles via tuning of the phosphine ligands and solvents under two optimized conditions are reported. The reaction follows a 1,4-Pd migration, aminopalladation, C(sp(2))-H activation, as well as five- and six-membered-ring fusion to form different products. The dihydroindeno[1,2,3-kl]acridine derivatives showed higher triplet energy (ET) levels than common blue phosphorescent dopant and may serve as good host candidates for blue triplet emitters.

The involvement of the trisulfur radical anion in electron-catalyzed sulfur insertion reactions: facile synthesis of benzothiazine derivatives under transition metal-free conditions.

An efficient and practical synthesis of benzothiazine by K2S initiated sulfur insertion reaction with enaminones via electron catalysis is developed. This protocol provides a new, environment-friendly and simple strategy to construct benzothiazine derivatives via formation of two C-S bonds under transition metal-free, additive-free and oxidant-free conditions. K2S not only provides the sulfur insertion source, but also ignites the reaction through the formation of a trisulfur radical anion and electrons in DMF.

tert-Butyl peroxybenzoate (TBPB)-mediated 2-isocyanobiaryl insertion with 1,4-dioxane: efficient synthesis of 6-alkyl phenanthridines via C(sp3)-H/C(sp2)-H bond functionalization.

An efficient method for the construction of 6-alkyl phenanthridines by tert-butyl peroxybenzoate (TBPB)-mediated 2-isocyanobiaryl insertion with 1,4-dioxane was established. Two new C-C bonds were formed in this reaction via a sequential C(sp(3))-H/C(sp(2))-H bond functionalization under metal-free conditions.