A Gold(I)-Catalyzed Hydroamination/Cycloisomerization Cascade: Concise Synthesis of (±)-seco-Antofine and (±)-Septicine

Synthesis of meta-Sulfonylpyridines via Copper(II)-Catalyzed Cascade Sulfonylation/Cyclization/Aromatization of Tertiary Enamides with Sulfonylhydrazides

A copper(II)-catalyzed radical cascade reaction of N-propargyl enamides with sulfonyl hydrazides was developed, which provided an unprecedented method for the direct synthesis of meta-sulfonylpyridines in high efficiency with good functional group compatibility and simple operation. Mechanistic studies indicated that this tandem process might be composed of the radical addition, intramolecular cyclization and oxidative aromatization.

Divergent Synthesis of Polysubstituted 1,2-Dihydropyridines and Pyridines through Manganese-Mediated Radical Cascade Cyclization of Tertiary Enamides

A Mn(III)-mediated radical cascade cyclization of N-propargyl enamides with sodium sulfinates was developed. Mechanistic studies indicated that this cascade process is mainly composed of the chemoselective addition of sulfonyl radical to C≡C bond and the regioselective intramolecular 6-endo-trig cyclization. This protocol provided a powerful method for the divergent synthesis of diverse polysubstituted meta-sulfonylpyridines or 1,2-dihydropyridines just by varying solvent and temperature featuring good functional group compatibility and simple operation.

Manganese(III)-Mediated Selective Cascade Phosphorylation-Cyclization of Tertiary Enamides for the Synthesis of Multi-Substituted 3-Phosphorylpyridines

A novel regioselective manganese(III)-mediated radical cascade cyclization of N-propargyl enamides with various H-phosphine oxides, H-phosphinates and H-phosphonates was developed. Mechanistic studies show that the reaction is mainly composed of the selective addition of phosphonyl radical to C≡C bond and the intramolecular 6-endo-trig cyclization of vinyl radical. Utilizing this protocol, we successfully synthesized a diverse range of 3-phosphorylpyridines in high efficiency with good functional group compatibility and simple operation.

Syntheses of Tetracyclic Indoline Derivatives Via Gold(I)-Catalyzed Hydroamination/Cycloisomerization Cascade of 2-Ethynyltryptamides

A gold(I)-catalyzed hydroamination/cycloisomerization cascade reaction was developed to yield indolizino[8,7-b]indole and indolo[2,3-a]-quinolizine derivatives from 2-ethynyltryptamides. The optimal conditions were determined by condition screening, and the functional group tolerances of these reactions were explored based on synthetic substrates. An insight into the explanation on the selectivity of the ring closure was obtained by density functional theory calculations. A plausible mechanism for the cascade reactions was proposed. Derivatization of the indolizino[8,7-b]indole and total synthesis of nauclefidine demonstrated the practicality of this strategy.

Copper Catalyst-Promoted Regioselective Multicomponent Cascade Cyclization of 3-Aza-1,5-enynes with Sulfur Dioxide and Cycloketone Oxime Esters to Access Cyanoalkylsulfonylated 1,2-Dihydropyridines

Radical cascade cyclization via the cracking of alkenyl C-H has emerged as an attractive and remarkable tool for the rapid construction of ring frameworks with endocyclic double bonds. We developed a cascade reaction of 3-aza-1,5-enynes with sulfur dioxide and cycloketone oxime esters to access cyanoalkylsulfonylated 1,2-dihydropyridines, which can be easily converted to pyridine derivatives. This protocol involves radical addition to the C≡C bond and 6-endo cyclization and features high regioselectivity and a broad substrate scope.

Post-Ugi Cyclizations Towards Polycyclic N-Heterocycles

The Ugi reaction has become one of the highly explored reactions for the formation of multifunctional adducts, due to the mild reaction conditions, wide scope and high variability. By carefully selecting the starting four components, Ugi-adducts could undergo different kinds of post-transformations for the synthesis of bioactive heterocycles, natural products and macrocycles. Considering the significance of polycycles, diverse post-Ugi transformations have been developed over the years for constructing structurally novel polycycles. In this account, we summarize important efforts for the synthesis of polycyclic N-heterocycles via post-Ugi cyclizations from the Van der Eycken laboratory onwards 2016. With the aid of transition metal catalysis from gold, rhodium, silver and palladium, as well as metal-free strategies, versatile polyheterocycles are prepared with high efficiency and step-economy.

Metal-Catalyzed Cascade Reactions between Alkynoic Acids and Dinucleophiles: A Review

Cascade reactions provide a straightforward access to many valuable compounds and reduce considerably the number of steps of a synthetic sequence. Among the domino and multicomponent processes that involve alkynes, the cascade reaction between alkynoic acids and C-, N-, O- and S-aminonucleophiles stands out as a particularly powerful tool for the one-pot construction of libraries of nitrogen-containing heterocyclic compounds with scaffold diversity and molecular complexity. This reaction, based on an initial metal-catalyzed cycloisomerization that generates an alkylidene lactone intermediate, was originally catalyzed by gold(I) catalysts, along with silver salts or Brönsted acid additives, but other alternative metal catalysts have emerged in the last decade as well as different reaction media. This review examines the existing literature on the topic of metal-catalyzed cascade reactions of acetylenic acids and dinucleophiles and discusses aspects concerning substrate/catalyst ratio for every catalyst system, nature of the aminonucleophile involved and substrate scope. In addition, alternative solvents are also considered, and an insight into the pathway of the reaction and possible intermediates is also provided.

Total Synthesis of Cryptopleurine and Its Analogues

Total synthesis of phenanthroquinolizidine alkaloid cryptopleurine was achieved in 8 steps from commercially available 2-pyridinecarboxaldehyde and the epoxide derived from methyleugenol. The key intermediate vinyl triflate enables the divergent synthesis of crypto­pleurine derivatives by late-stage installation of various substituents on the C-ring.

The synthesis of diverse benzazepinoindoles via gold-catalyzed post-Ugi alkyne hydroarylation/Michael addition sequence

By combining an Ugi-4CR and a gold-catalyzed cascade cyclization, diverse benzazepinoindoles are assembled in a step-economical, chemo- and regioselectivity fashion.

"Golden" Cascade Cyclization to Benzo[c]-Phenanthridines

Herein, we describe a gold-catalyzed cascade cyclization of Boc-protected benzylamines bearing two tethered alkyne moieties in a domino reaction initiated by a 6-endo-dig cyclization. The reaction was screened intensively, and the scope was explored, resulting in nine new Boc-protected dihydrobenzo[c]phenanthridines with yields of up to 98 %; even a π-extension and two bidirectional approaches were successful. Furthermore, thermal cleavage of the Boc group and subsequent oxidation gave substituted benzo[c]phenanthridines in up to quantitative yields. Two bidirectional approaches under the optimized conditions were successful, and the resulting π-extended molecules were tested as organic semiconductors in organic thin-film transistors.

Palladium-Catalyzed Arylative Dearomatization and Subsequent Aromatization/Dearomatization/Aza-Michael Addition: Access to Zephycarinatine and Zephygranditine Skeletons

We have developed a novel palladium-catalyzed arylative dearomatization and subsequent aromatization/dearomatization/aza-Michael addition process of Ugi adducts, enabling the rapid construction of diverse zephycarinatine and zephygranditine scaffolds containing two adjacent quaternary carbon stereocenters with excellent chemoselectivity and stereoselectivity in a rapid, step-economical, and highly efficient manner. This approach shows broad substrate scope and excellent functional-group tolerance with diverse electron-rich and electron-deficient aromatic substrates. The synthetic utility of this method is further demonstrated by versatile transformations of the products.

Zn(OTf)2-catalyzed hydroamination of ynamides with aromatic amines

The Zn(OTf)₂-catalyzed hydroamination of ynamides 2a-2l with aromatic amines 1a-1r was developed. This protocol features broad substrate scope of aromatic amines, good functional group tolerance for ynamides, and excellent regioselectivities. As a result, a variety of substituted amidine compounds 3aa-3oa, 3ab-3al and 3pa-3rk were prepared in moderate to excellent yields and with high regioselectivities.