Metal-Free Temperature-Controlled Intermolecular [3 + 2] Annulation to Access Benzo[d]thiazole-2(3H)-thiones and Benzo[d]thiazol-2(3H)-ones

Photocatalytic One-Pot Three-Component Reaction for the Regioselective Synthesis of Bromo-Substituted Pyrazoles

A photocatalytic three-component cascade reaction of readily available enaminones, hydrazines, and CBr4 for the synthesis of bromo-substituted pyrazoles in one pot has been demonstrated. This strategy involves intermolecular C-N/C-Br bond formation and represents an efficient approach to the construction of 4-bromo-substituted pyrazoles with high regioselectivity, broad substrate scope, good functional group tolerance, convenient operation, and mild reaction conditions. Mechanistic investigations show that this reaction proceeds via intermolecular cyclization of enaminones with hydrazines, followed by a regioselective bromination of pyrazoles using CBr4 as a "Br" source.

Copper-Catalyzed Domino-Double Annulation of o-Aminobenzamides with 2-Iodoisothiocyanates for the Synthesis of 12H-Benzo[4,5]thiazolo[2,3-b]quinazolin-12-ones

A facile and efficient copper-catalyzed domino-double annulation strategy was developed from easily accessible o-aminobenzamides and 2-iodoisothiocyanates, which affords a direct pathway for the synthesis of tetracyclic fused 12H-benzo[4,5]thiazolo[2,3-b]quinazolin-12-ones in moderate to good yields without the addition of ligands, bases, and external oxidants. The reaction involves a C-N bond cleavage and the formation of a C-N/C-S bond in one step with the advantages of using an inexpensive copper catalyst and easy operation. Mechanistic studies suggest that this transformation proceeds via intermolecular condensation of o-aminobenzamides with 2-iodoisothiocyanates, followed by an intramolecular Ullmann-type cross-coupling cyclization reaction.

Copper-Promoted Aerobic Oxidative [3+2] Cycloaddition Reactions of N,N-Disubstituted Hydrazines with Alkynoates: Access to Substituted Pyrazoles

A copper-promoted aerobic oxidative [3+2] cycloaddition reaction for the synthesis of various substituted pyrazoles from N,N-disubstituted hydrazines with alkynoates in the presence of bases is developed. This work involves a direct C(sp³)-H functionalization and the formation of new C-C/C-N bonds. In this strategy, inexpensive and easily available Cu₂O serves as the promoter and air acts as the green oxidant. The reaction exhibits the advantages of high atom and step economy, high regioselectivity, and easy operation.

DBU-Promoted Deaminative Thiolation of 1H-Benzo[d]imidazol-2-amines and Benzo[d]oxazol-2-amines

A facile and efficient catalyst-/metal-/oxidant-free DBU-promoted deaminative thiolation reaction of 1H-benzo[d]imidazol-2-amines and benzo[d]oxazol-2-amines has been developed at room temperature conditions in a one-pot protocol. This practical three-component strategy represents a novel and environmentally friendly reaction pathway toward the straightforward synthesis of various 2-thio-1H-benzo[d]imidazoles and 2-thiobenzo[d]oxazoles using carbon disulfide as a sulfur source through C-N bond cleavage and C-S bond formation process. Different types of 1H-benzo[d]imidazol-2-amines, benzo[d]oxazol-2-amines, and organic bromides are suitable substrates. The gram-scale and late-stage modification experiments provide the potential applications based on this methodology in the field of organic and medicinal chemistry.