Facile Synthesis of Polysubstituted Imidazoles through CBr4-Mediated Tandem Cyclization of Amidines with 1,3-Dicarbonyl Compounds or Ketones

Copper-Catalyzed Defluorinative [3 + 2] Cyclization of Amidines and Trifluoromethyl Carbenoids for the Synthesis of 5-Fluoroimidazoles

A Cu-catalyzed [3 + 2] cyclization of amidines with trifluoromethyldiazo compounds is described. The reaction affords 5-fluoroimidazoles in good yields by cleaving dual C-F bonds in a CF3 group. Using 2-aminoazo heterocycles as the substrates, various annelated imidazoles containing a fluorine atom were also constructed by this method without changing the conditions. The resultant 5-fluoroimidazoles show high reactivity toward SNAr reactions with a series of nucleophiles.

Ketones as strategic building blocks for the synthesis of natural product-inspired compounds

Natural product-inspired compound collections serve as excellent sources for the identification of new bioactive compounds to treat disease. However, such compounds must necessarily be more structurally-enriched than traditional screening compounds, therefore inventive synthetic strategies and reliable methods are needed to prepare them. Amongst the various possible starting materials that could be considered for the synthesis of natural product-inspired compounds, ketones can be especially valuable due to the vast variety of complexity-building synthetic transformations that they can take part in, their high prevalence as commercial building blocks, and relative ease of synthesis. With a view towards developing a unified synthetic strategy for the preparation of next generation bioactive compound collections, this review considers whether ketones could serve as general precursors in this regard, and summarises the opulence of synthetic transformations available for the annulation of natural product ring-systems to ketone starting materials.

One-Pot Three-Component Coupling Reaction of α-Amino Aryl Ketones, Indoles, and Perbromomethane Under Mild Conditions

A simple and efficient one-pot three-component cascade reaction of α-amino aryl ketones, indoles, and CBr₄ in moderate to good yields has been developed. This new strategy exhibits excellent mild reaction conditions and step-economy, easily accessible reactants, and simultaneous construction of three different new bonds (C=N, C–C, and N-Br) in a single step. It is worth noting that the protocol developed provides a simple and practical tool for the construction of diverse indole-containing heterocyclic frameworks, indicating its potential applications in medicinal and material chemistry.

Dibromination of Cinnamamides with CBr4 Under Mild Conditions

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A novel, mild and efficient protocol to synthesize dibrominated propanamides has been developed. The presented methodology provides several merits, such as easy-to-handle and stable brominated substrate, catalyst-free, additive free and facile experimental operation. The preliminary mechanism study indicated that a free radical pathway might be involved in the presented reaction.

CBr4 Mediated [4 + 1] Dehydrocyclization for the Synthesis of Functionalized Imidazo[1,5-a]heterocycles from Pyridin-2-ylmethanamines and Aldehydes

A CBr₄ mediated [4 + 1] dehydrocyclization was developed for the synthesis of imidazo[1,5-a]heterocycles from pyridin-2-ylmethanamines and aldehydes. This method was highly practical with the advantages of wide substrate scope, functional group tolerance, and mild reaction conditions.

Construction of a novel asymmetric imidazole-cored AIE probe for ratiometric imaging of endogenous leucine aminopeptidase

We report a rational strategy to deliberately construct the first asymmetric tetraarylimidazole-based AIE probe, integrating AIE behavior in synergy with ESIPT character to image endogenous LAP for the first time. It offered good sensitivity and selectivity, and concomitantly, was applied successfully for real-time tracking of LAP in the cisplatin-induced liver injury zebrafish model.

Direct intramolecular double cross-dehydrogentive-coupling (CDC) cyclization of N-(2-pyridyl)amidines under metal-free conditions

A facile transition-metal-free protocol to form 2-iminoimidazo[1, 2-a]-pyridines bearing a -CHBr₂ group and an aza-quaternary carbon center at the 3 position from N-(2-pyridyl)amidines substrates, in which the new heterocyclic skeletons constructed from amidines via radical reactions or nucleophilic substitution reactions are promoted only by CBr₄ under mild conditions, is demonstrated. The reactions were realized by intramolecular CDC reaction involving C-N and C-C bond formation via the sequential C(sp³)-H bifunctionalization mode on the same carbon atom under mild conditions. Moreover, this work also provides an excellent and representative example for CBr₄ as an efficient reagent to initiate radical reactions under initiator-free conditions or to give rise to nucleophilic substitution reactions only by base.

An efficient synthesis of benzothiazole using tetrabromomethane as a halogen bond donor catalyst

A CBr₄ catalyzed simple, mild, and efficient protocol has been developed for the synthesis of 2-substituted benzothiazole from 2-aminothiophenols and N-methylthioamides under solvent free conditions.

Tandem radical cyclization of N-methacryloyl benzamides with CBr4 to construct brominated isoquinolinediones

A simple cumene (isopropylbenzene, IPB) promoted auto-oxidation involved tandem radical cyclization of N-methacryloyl benzamides using stable and easy-to-handle CBr₄ as the bromine source is described. This strategy provides an efficient and practical approach for the synthesis of bromine containing isoquinolinediones. This method also presents a new way to generate bromine radicals using a mild auto-oxidation pathway.

CBr4-mediated cross-coupling reactions of α-amino carbonyl compounds with alcohols and thiols to build C–O and C–S bonds, respectively

The direct C(sp³)–H bond functionalization of α-amino carbonyl compounds with CBr₄ to construct C–O and C–S bonds.

Tandem radical cyclization to construct poly-brominated 2-oxindoles

A metal-free aerobic way to construct tribromomethylated poly-brominated 2-oxindoles from reaction of N-arylacrylamides with CBr₄via a tandem radical cyclization process was discovered. The formation of the 1,1-dibromoolefin derivatives was also realized at higher temperature.

A divergent and metal free synthesis of sulfoximine tethered imidazoles, imidazopyridines, imidazothiazoles, imidazobenzothiazines, thiazoles and selenazoles

A divergent and metal free approach has been successfully developed for the synthesis of sulfoximine tethered heterocycles from a α-bromoalkanone building block.

Imidazole synthesis by transition metal free, base-mediated deaminative coupling of benzylamines and nitriles

An unprecedented transition metal free, base-mediated deaminative coupling of benzylamines and nitriles is reported. This protocol provides a practical strategy for the synthesis of 2,4,5-tri-substituted imidazoles with liberation of NH₃.