Catalytic σ-activation of carbon-carbon triple bonds: reactions of propargylic alcohols and alkynes.

The majority reactions of alkynes in the literature are reported to proceed via either structural σ-activation or catalytic π-activation of C≡C bonds. We skillfully designed novel methods for the catalytic σ-activation of C≡C bonds of alkynyl compounds. For terminal alkynyl compounds, σ-activation was achieved by silver(i)-catalyzed C-H functionalization. Whereas σ-activation of internal alkynes was accomplished by the generation of propargylic cations from propargylic alcohols under Lewis-acid catalysis. These σ-activated species have been successfully used for new C-C and C-heteroatom bond formation reactions. Plausible reaction pathways were proposed based on typical control experiments to help the readers to gain insights into reactions and for further discovery of new reactions based on this concept of catalytic σ-activation of C≡C bonds.

Silver-Catalyzed Isocyanide-Isocyanide [3+2] Cross-Cycloaddition Involving 1,2-Group Migration: Efficient Synthesis of Trisubstituted lmidazoles.

Imidazole ring is an important five-membered aromatic heterocycle that is widely present in natural products and synthetic molecules. The isocyanide-isocyanide [3+2] cross-cycloaddition reaction constitutes a straightforward method to access imidazoles starting from the easily available chemicals. So far, only three successive reports are known and all lead to the formation of 1,4-disubstituted imidazoles. Here, we report the first isocyanide-isocyanide [3+2] cross-cycloaddition reaction allowing for the formation of 1,4,5-trisubstituted imidazoles under silver catalysis. An unexpected 1,2-migration of sulfonyl, alkoxycaybonyl, and carbamoyl groups took place during the cyclization process that is responsible for the formation of trisubstituted imidazoles. This report displayed a mechanistically novel synthetic method toward a variety of imidazole derivatives, which are otherwise difficult to access by conventional methods.

Chemo- and regioselective reductive deoxygenation of 1-en-4-yn-ols into 1,4-enynes through FeF3 and TfOH co-catalysis.

We report chemo- and regioselective direct reductive deoxygenation of 1-en-4-yn-3-ols into 1,4-enynes through FeF3 and TfOH cooperative catalysis under NBSH-mediated conditions. Further, we show the efficient synthesis of a pharmaceutically significant 1,4-enyne. The present methodology can also be used for chemo- and regioselective direct deoxygenation of other alcohols.

Synthesis of 4-Ynamides and Cyclization by the Vilsmeier Reagent to Dihydrofuran-2(3H)-ones.

The room-temperature nucleophilic addition of vinyl azides to propargylic alcohols under BF3·Et2O catalysis provides an efficient synthesis of 4-ynamides. The procedure is operationally convenient, shows broad substrate scope, and is viable for the synthesis of multifunctional 4-ynamides. Further, a Vilsmeier intramolecular cyclization of 4-ynamides into dihydrofuran-2(3H)-ones has also been discovered, which represents the first report of alkynes being used as the nucleophiles in Vilsmeier-type reactions.

Iodobenzene catalyzed C-H amination of N-substituted amidines using m-chloroperbenzoic acid.

The oxidative C-H amination of N"-aryl-N'-tosyl/N'-methylsulfonylamidines and N,N'-bis(aryl)amidines has been accomplished using iodobenzene as a catalyst to furnish 1,2-disubstituted benzimidazoles in the presence of mCPBA as a terminal oxidant at room temperature. The reaction is general, and the target products can be obtained in moderate to high yields.

Pd-catalyzed C-H activation/C-N bond formation: a new route to 1-aryl-1H-benzotriazoles.

A method for the C-H activation of aryl triazene compounds followed by intramolecular amination is described. It involves the use of a catalytic amount of Pd(OAc)(2) that efficiently effects the cyclization to provide 1-aryl-1H-benzotriazoles at moderate temperature.