Zinc-Catalyzed Alkyne Oxidation/C-H Functionalization: Highly Site-Selective Synthesis of Versatile Isoquinolones and β-Carbolines

Gold-Catalyzed Oxidation Terminal Alkyne: An Approach to Synthesize Substituted Dihydronaphthalen-2(1H)-ones and Phenanthrenols

A facile gold-catalyzed oxidation terminal alkynes to synthesize substituted dihydronaphthalen-2(1H)-ones 3 and phenanthrenols 5 was realized. Various useful structures and drug precursors were generated in up to 99% yield under mild condition and low catalyst loading.

PIFA-BF3·OEt2 mediated intramolecular regioselective domino cyclization of ynamides: A novel method for the synthesis of tetrahydroisoquinoline-oxazol-2(3H)-ones

The transition metal-free intramolecular regioselective domino cyclization of N-Boc protected ynamides has been developed to provide the corresponding tetrahydroisoquinoline-oxazo-2(3H)-ones in moderate to good yields.

Metal-Free Formal Oxidative C-C Coupling by In Situ Generation of an Enolonium Species

Much contemporary organic synthesis relies on transformations that are driven by the intrinsic, so-called "natural", polarity of chemical bonds and reactive centers. The design of unconventionally polarized synthons is a highly desirable strategy, as it generally enables unprecedented retrosynthetic disconnections for the synthesis of complex substances. Whereas the umpolung of carbonyl centers is a well-known strategy, polarity reversal at the α-position of a carbonyl group is much rarer. Herein, we report the design of a novel electrophilic enolonium species and its application in efficient and chemoselective, metal-free oxidative C-C coupling.

Yttrium-Catalyzed Intramolecular Hydroalkoxylation/Claisen Rearrangement Sequence: Efficient Synthesis of Medium-Sized Lactams

An efficient yttrium-catalyzed intramolecular hydroalkoxylation/Claisen rearrangement sequence has been achieved, thus enabling facile access to a diverse array of valuable medium-sized lactams. Furthermore, a mechanistic rationale for this novel cascade reaction is well supported by a variety of control experiments.

Brønsted Acid Catalyzed Oxygenative Bimolecular Friedel-Crafts-type Coupling of Ynamides

A non-metal approach for accessing α-oxo carbene surrogates for a C-C bond-forming bimolecular coupling between ynamides and nucleophilic arenes was developed. This acid-catalyzed coupling features mild temperature, which is critical for the required temporal chemoselectivity among nucleophiles. The scope of nucleophiles includes indoles, pyrroles, anilines, phenols and silyl enolethers. Furthermore, a direct test of S_N 2' mechanism has been provided by employing chiral N,N'-dioxides which also enlightens the nature of the intermediates in related metal-catalyzed processes.

Gold-Catalyzed Regiodivergent [2 + 2 + 2]-Cycloadditions of Allenes with Triazines

Gold-catalyzed regiodivergent cycloadditions of functionalized allenes with 1,3,5-triazines, providing diverse N-heterocycles in moderate to excellent yields under mild reaction conditions, are reported. Importantly, different types of allenes exhibit distinct selectivity and reactivity for the reactions. Mechanistic investigations reveal that all of the cycloadditions proceed through a stepwise [2 + 2 + 2]-cycloaddition process.

Brønsted acid-catalyzed α-halogenation of ynamides from halogenated solvents and pyridine-N-oxides

The keteniminium ions generated from the protonation of ynamides formed reversible adducts with counter anions and pyridine-N-oxides as well as halogenated solvents.

Synthesis of 5-Iodo-1,2,3,4-tetrahydropyridines by Rhodium-Catalyzed Tandem Nucleophilic Attacks Involving 1-Sulfonyl-1,2,3-triazoles and Iodides

Sodium iodide is used for the first time as a nucleophile to trap an α-imino rhodium carbene, which triggers a tandem process involving intermolecular nucleophilic attack and intramolecular S_N2 reaction. A series of 5-iodo-1,2,3,4-tetrahydropyridines are obtained in high yield, and the synthetic utility of the products is demonstrated in cross-coupling reactions and the construction of biorelated polycyclic compounds.

Synthesis of Barbaralones and Bullvalenes Made Easy by Gold Catalysis

The gold(I)-catalyzed oxidative cyclization of 7-ethynyl-1,3,5-cycloheptatrienes gives 1-substituted barbaralones in a general manner, which simplifies the access to other fluxional molecules. As an example, we report the shortest syntheses of bullvalene, phenylbullvalene, and disubstituted bullvalenes, and a readily accessible route to complex cage-type structures by further gold(I)-catalyzed reactions.

Synthesis of 2-Aza-1,3-butadienes through Gold-Catalyzed Intermolecular Ynamide Amination/C-H Functionalization

A novel gold-catalyzed tandem intermolecular ynamide amination/C-H functionalization has been developed. A variety of highly functionalized 2-aza-1,3-butadienes can be obtained readily by utilizing this strategy. In addition, α-imino gold carbene intermediates are proposed in this amination reaction and with support by DFT (density functional theory) calculations.

Metal-free intermolecular formal cycloadditions enable an orthogonal access to nitrogen heterocycles

Nitrogen-containing heteroaromatic cores are ubiquitous building blocks in organic chemistry. Herein, we present a family of metal-free intermolecular formal cycloaddition reactions that enable highly selective and orthogonal access to isoquinolines and pyrimidines at will. Applications of the products are complemented by a density functional theory mechanistic analysis that pinpoints the crucial factors responsible for the selectivity observed, including stoichiometry and the nature of the heteroalkyne.

Generation of Oxazolidine-2,4-diones Bearing Sulfur-Substituted Quaternary Carbon Atoms by Oxothiolation/Cyclization of Ynamides

A novel method for metal-free oxothiolation of ynamides to construct oxazolidine-2,4-diones bearing sulfur-substituted quaternary carbon atoms has been developed. It represents a rare C-O bond cleavage of ynamides, as well as a facile and tandem approach for the formation of C-O, C-S, and C-Cl bonds. This redox-neutral protocol can be applied to the synthesis of multisubstituted oxazolidine-2,4-diones with good chemoselectivity and good yields of isolated products under mild conditions.

Recent progress towards gold-catalyzed synthesis of N-containing tricyclic compounds based on ynamides

The recent advances in the gold-catalyzed construction of N-containing tricycles based on ynamides are reviewed by highlighting their specificity and applicability, and the mechanistic rationale.

Synthesis of fused isoquinolines via gold-catalyzed tandem alkyne amination/intramolecular O–H insertion

A novel gold-catalyzed tandem alkyne amination/intramolecular O–H insertion has been developed. A variety of [1,4]oxazino[3,2-c]isoquinolines are readily accessed under mild reaction conditions by utilizing this strategy, thereby providing an efficient and practical route for the construction of synthetically useful fused isoquinolines.

Zn/Sc bimetallic relay catalysis: one pot cycloisomerization/carbonyl–ene reaction toward oxazole derivatives

A novel tandem metal relay catalytic system combining Zn(ii)-catalyzed cycloisomerization and a Sc(iii)-catalyzed carbonyl–ene reaction has been successfully developed.

A zinc-catalyzed oxidative reaction of ynamides with phenols and thiophenols: highly site-selective synthesis of versatile α-aryloxy amides and α-arylthio amides

A zinc-catalyzed oxidative reaction of ynamides with phenols and thiophenols under mild reaction conditions has been developed, which provides various α-aryloxy amides and α-arylthio amides in moderate to good yields, respectively. Importantly, high chemoselectivity is achieved by such a non-noble metal-catalyzed alkyne oxidation.

Synthesis of α,β-Unsaturated N-Sulfonyl Imides through Zinc-Catalyzed Intermolecular Oxidation of N-Sulfonyl Ynamides

A novel zinc-catalyzed intermolecular oxidation of N-sulfonyl ynamides has been developed. A variety of functionalized α,β-unsaturated N-sulfonyl imides are readily accessed by utilizing this approach, thus providing a viable alternative to synthetically useful α,β-unsaturated imides. Importantly, the reaction is proposed to proceed by a vinyligous E2-type elimination pathway, but not metal carbene pathway.