Copper-Catalyzed Intramolecular Annulation of Conjugated Enynones to Substituted 1 H-Indenes and Mechanistic Studies.

Herein, a copper-catalyzed intramolecular cascade reaction of conjugated enynones to deliver substituted 1 H-indenes is reported. The inexpensive and less toxic copper salt served as the only catalyst in the transformation, affording the 3-(2-furyl)-substituted 1 H-indenes in good to excellent yields under mild reaction conditions with broad functional group tolerance and making it highly appealing for synthetic organic chemistry. Notably, detailed DFT calculations have been carried out to elucidate that the reaction undergoes a copper-mediated 5- exo-dig cyclization of enynones to afford copper-(2-furyl)-carbene intermediate, followed by diene-carbene cyclization (one step but involving 6π cyclization of Cu-carbene and reductive elimination) and 1,5-hydrogen shift to provide the 1 H-indenes.

Gold-catalyzed Bicyclization of Diaryl Alkynes: Synthesis of Polycyclic Fused Indole and Spirooxindole Derivatives.

An unprecedented gold-catalyzed bicyclization reaction of diaryl alkynes has been developed for the synthesis of indoles in good to high yields. Mechanistically, this alkyne bifunctionalization transformation was terminated by a stepwise formal X-H insertion reaction to furnish the corresponding polycyclic-frameworks with structural diversity, and the key intermediate 3 H-indole was isolated and characterized for the first time. In addition, further transformation of these generated tetracyclic-indoles with PCC as the oxidant provided straightforward access to the spirooxindoles in high yields.

Ligand-Free, Cu- and Fe-Catalyzed Selective Ring-Opening Arylations of Benzoxazoles with Aryl Iodides.

Cu- or Fe-based catalyst systems have been reported to selectively catalyze the N,N-diarylation or N-monoarylation of benzoxazoles ring-opening with aryl iodides in the absence of additional added ligand in polyethylene glycol under an inert atmosphere. Two types of coupling products (triphenylamines and diphenylamines) have been examined and the reaction routes can be simply controlled by changing the metal salts (Cu or Fe) as catalyst. A range of substrates have been investigated for the diverse reactions, and the corresponding arylation products were achieved in good to high yields.

The Application of Copper/Iron Cocatalysis in Cross-Coupling Reactions.

For conventional cross-couplings in organic chemistry, precious metal (such as Pd or Rh) complexes have been the preferable choices as catalysts. However, their high cost, toxicity, and potential contamination of products limit their massive applications on some occasions, particularly in the pharmaceutical industry, where close monitoring of the metal contamination of products is required. Therefore, the use of metals that are less expensive and less toxic than Pd or Rh can be greatly advantageous and earth abundant metal (such Fe or Cu) catalysts have shown promise for replacing the precious metals.

NaI-Mediated Acetamidosulphenylation of Alkenes with Nitriles as the Nucleophiles: A Direct Access to Acetamidosulfides.

An example of a transition-metal-free, direct, and efficient acetamidosulphenylation reaction of alkenes using nitriles as the nucleophiles via a radical process is presented. This reaction shows a broad substrate scope and high regioselectivity and provides straightforward access to acetamidosulfide derivatives in moderate to high yields.

Cu-Catalyzed direct cyanation of terminal alkynes with AMBN or AIBN as the cyanation reagent.

A Cu-catalyzed direct cyanation of terminal alkynes was reported with broad substrate generality in moderate to high yield, and AMBN (azobisisoamylonitrile)/AIBN (azobisisobutyronitrile) were used as less toxic and effective cyanating sources in open air. Interestingly, addition products were selectively achieved as the major product under the same conditions in argon.

Phosphoric Acid-Mediated Synthesis of Vinyl Sulfones through Decarboxylative Coupling Reactions of Sodium Sulfinates with Phenylpropiolic Acids.

A novel phosphoric acid -mediated synthesis of vinyl sulfones through decarboxylative coupling reactions of sodium sulfinates with phenylpropiolic acids is described. This transformation is efficient and environmentally friendly.

A NCS mediated oxidative C-H bond functionalization: direct esterification between a C(sp(3))-H bond and carboxylic acids.

A transition metal free oxidative C-H bond functionalization/esterification of α-alkoxy alkanes with acids is described in this report. This method is effectively mediated by NCS instead of traditional oxidants, like TBHP or its derivatives, and directly generates the esterification products in moderate to high yield under mild conditions. This tranformation constitutes a practical and general approach toward various α-acyloxy ethers with broad substrate generality; alkyl-, aryl-, alkenyl- and alkynyl-carboxylic acids are all well tolerated.

Iron/Copper co-catalyzed synthesis of vinyl sulfones from sulfonyl hydrazides and alkyne derivatives.

A new approach to the selective synthesis of (E)-vinyl sulfones has been developed via a Fe/Cu co-catalyzed sulfonylation of arylpropiolic acid or phenylacetylene with sulfonyl hydrazides. A variety of vinyl sulfones have been obtained in moderate to good yields, comparable to the best results reported so far. The inexpensive Fe/Cu co-catalyzed method features a simple experimental procedure and good tolerance of substrate.

Stereoselective intermolecular nitroaminoxylation of terminal aromatic alkynes: trapping alkenyl radicals by TEMPO.

The vinyl radical is one of the most unstable organic radicals. It is demonstrated that a nitro radical attacks phenylacetylene and makes the phenyl ring deconjugated with a double bond so that the resulting vinyl radical may be stabilized by delocalization to the phenyl ring's π orbital and easily trapped by TEMPO. It is noteworthy that all desired products were obtained in moderate to good yields in an (E)-configuration.

Functionalization of amides via copper-catalyzed oxyalkylation of vinylarenes and decarboxylative alkenylation of sp3 C-H.

An efficient protocol was developed to prepare a series of derivatives from amides by copper-catalyzed oxyalkylation of vinylarenes and decarboxylative alkenylation of sp(3) C-H. This method is simple, practical, and inexpensive.

Transition-metal-free synthesis of N-(1-alkenyl)imidazoles by potassium phosphate-promoted addition reaction of alkynes to imidazoles.

The addition reaction of alkynes to N-heterocycles by simply heating in DMSO with potassium phosphate is reported. Good yields with high stereoselectivity could be achieved for a range of substrates. The scope is quite general for both amines and phenylacetylenes.

Copper-catalyzed methyl esterification reactions via C-C bond cleavage.

The highly effective synthesis of methyl esters from benzylic alcohols, aldehydes, or acids via copper-catalyzed C-C cleavage from tert-butyl hydroperoxide is reported in this paper for the first time. Our protocol is easily accessible and practical, making it a possible supplement for the traditional way.