New tandem catalysis: preparation of cyclic enol ethers through a ruthenium-catalyzed ring-closing metathesis-olefin isomerization sequence

All-in-One Synthesis of 3,6-Dideoxysugars: An Olefin Metathesis-Isomerization Approach

A collective synthesis of 3,6-dideoxysugars, including seven naturally known congeners, has been reported using commercially available methyl lactates in five steps. The essential tandem process involving the olefin cross-metathesis and isomerization steps was enabled by the dual function of Grubbs-II catalyst, affording the products in good yields and providing concise and practical access to a class of biologically important deoxysugars.

Palladium-Catalyzed Aminomethylation and Cyclization of Enynol to O-Heterocycle Confined 1,3-Dienes

The rational tuning of the electrophilicity of the allylpalladium intermediates enables the regioselectively intramolecular 1,2-addition of enynol in the presence of aminal. This aminomethylation and cyclization reaction via C-N bond activation and intramolecular nucleophilic addition provides a rare example for the synthesis of O-containing heterocycle-confined 1,3-dienes, which is of synthetic potential for further derivatization. The method possesses broad substrate generality as well as functional group compatibility and efficiently affords a wide range of desired products with 5-, 6-, and 8-membered O-containing heterocycles with various functional groups.

Ring-closing metathesis of N-alkenyl-cyanamides

An entry to new classes of nitrogen-containing heterocycles featuring both a cyanamide and an unsaturated 5-, 6- or 7-membered ring is reported by RCM of the corresponding N-alkenyl-cyanamides, new partners for olefin metathesis.

Dual Activity of Grubbs-Type Catalyst in the Transvinylation of Carboxylic Acids and Ring-Closing Metathesis Reactions

The development of a multifunctional catalyst, which mimics the promiscuity of enzymes, that would catalyze more than one chemical transformation in a single reaction vessel is one of the key points of modern sustainable chemistry. The results of our experiments indicated that Grubbs-type catalysts possess such multitask activity, catalyzing the transvinylation reaction of carboxylic acids without losing their original metathetic activity. This new activity of Grubbs catalysts was evidenced on several examples. It allows us to design a transvinylation/ring-closing metathesis (RCM) cascade reaction leading to the formation of endocyclic enol lactones from unsaturated carboxylic acids in an one-pot procedure. This unique ability of Grubbs catalyst to catalyze multiple mechanically distinct cascade reactions in a chemoselective way offers the new possibility for the synthesis of complex compounds from simple, easily accessible substrates.

2-Methyltetrahydrofuran as a Solvent of Choice for Spontaneous Metathesis/Isomerization Sequence

A new protocol for ring-closing metathesis/isomerization sequence was developed. The reactions of selected dienes were performed in overheated 2-methyltetrahydrofuran at 120 °C and provided a wide range of cyclic vinyl ethers and amides with good yields and selectivities. Computational analysis suggests that the relative yield of products depends on a thermodynamically driven process on the basis of relative stabilities of isomers.

Ruthenium-Catalyzed Intramolecular Double Hydroalkoxylation of Internal Alkynes

Intramolecular double hydroalkoxylation of internal alkynes could be achieved using a Grubbs-type ruthenium carbene complex or its modified species to deliver a series of bridged- and spiroacetal derivatives in moderate to good yields. This study represents a new example of nonmetathetic reactions catalyzed by Grubbs-type ruthenium carbene complexes.

Stereodivergent approach in the protected glycal synthesis of L-vancosamine, L-saccharosamine, L-daunosamine and L-ristosamine involving a ring-closing metathesis step

In this paper, a new access to several chiral 3-aminoglycals as potential precursors for glycosylated natural products is reported from a common starting material, (−)-methyl-L-lactate. The stereodivergent strategy is based on the implementation of a ring-closing metathesis of vinyl ethers as key step of reaction sequences developed.

Design of a Selective Ring-Closing Enyne Metathesis-Reduction for the Generation of Different Synthetic Scaffolds

A tandem process of ring-closing enyne metathesis (RCEYM)-reduction using modern ruthenium catalysts and a hydrogen donor is described. This straightforward methodology is useful for C(sp³) generation under mild reaction conditions. Variables such as solvent, catalyst, hydride source, and temperature were adjusted toward the exclusive formation of different products.

Ethenolysis: A Green Catalytic Tool to Cleave Carbon-Carbon Double Bonds

Remarkable innovations have been made in the field of olefin metathesis due to the design and preparation of new catalysts. Ethenolysis, which is cross-metathesis with ethylene, represents one catalytic transformation that has been used with the purpose of cleaving internal carbon-carbon double bonds. The objectives were either the ring opening of cyclic olefins to produce dienes or the shortening of unsaturated hydrocarbon chains to degrade polymers or generate valuable shorter terminal olefins in a controlled manner. This Review summarizes several aspects of this reaction: the catalysts, their degradation in the presence of ethylene, some parameters driving their productivity, the side reactions, and the applications of ethenolysis in organic synthesis and in potential industrial applications.

Chemodivergent, One-Pot, Multi-Component Synthesis of Pyrroles and Tetrahydropyridines under Solvent- and Catalyst-Free Conditions Using the Grinding Method

A highly efficient, chemoselective synthesis of a library of polysubstituted pyrroles and tetrahydropyridines has been achieved through the one-pot, multicomponent reactions of ethyl (E)-3-(aryl/alkyl amino) acrylates, 2,2-dihydroxy-1-arylethan-1-ones, and malononitrile under solvent- and catalyst-free grinding conditions. The selective formation of pyrrole or tetrahydropyridines relied on substitution of the N-aryl of ethyl (E)-3-(4-arylamino) acrylates. These reactions presumably occurred via a domino Knoevenagel condensation and Michael addition followed by an intramolecular cyclization sequence of reactions in a single transformation.

A Light-Activated Olefin Metathesis Catalyst Equipped with a Chromatic Orthogonal Self-Destruct Function

A sulfur-chelated photolatent ruthenium olefin metathesis catalyst has been equipped with supersilyl protecting groups on the N-heterocyclic carbene ligand. The silyl groups function as an irreversible chromatic kill switch, thus decomposing the catalyst when it is irradiated with 254 nm UV light. Therefore, different types of olefin metathesis reactions may be started by irradiation with 350 nm UV light and prevented by irradiation with shorter wavelengths. The possibility to induce and impede catalysis just by using light of different frequencies opens the pathway for stereolithographic applications and novel light-guided chemical sequences.

Development of an Enyne Metathesis/Isomerization/Diels-Alder One-Pot Reaction for the Synthesis of a Novel Near-Infrared (NIR) Dye Core

N-Alkyl-N-allyl-2-alkynylaniline derivatives undergo a tandem ring-closing enyne metathesis/isomerization/Diels-Alder cycloaddition sequence in the presence of a second-generation Grubbs catalyst and dienophiles. In practice, the acyclic enyne in the presence of the ruthenium alkylidene first undergoes ring-closing metathesis to generate cyclic 4-vinyl-1,2-dihydroquinolines; following diene isomerization and then the addition of a dienophile, these ring-closing metathesis products are selectively converted into a 7-methyl-4H-naphtho[3,2,1-de]quinoline-8,11-dione core. Overall, the reaction sequence converts simple aniline derivatives into π-conjugated small molecules, which have characteristic absorption in the near-infrared region, in a single operation through three unique ruthenium-catalyzed transformations.

Tandem Z-Selective Cross-Metathesis/Dihydroxylation: Synthesis of anti-1,2-Diols

A stereoselective synthesis of anti-1,2-diols has been developed using a multitasking Ru catalyst in an assisted tandem catalysis protocol. A cyclometalated Ru complex catalyzes first a Z-selective cross-metathesis of two terminal olefins, followed by a stereospecific dihydroxylation. Both steps are catalyzed by Ru, as the Ru complex is converted to a dihydroxylation catalyst upon addition of NaIO4. A variety of olefins were transformed into valuable, highly functionalized, and stereodefined molecules. Mechanistic experiments were performed to probe the nature of the oxidation step and catalyst inhibition pathways. These experiments point the way to more broadly applicable tandem catalytic transformations.

One-pot isomerization-cross metathesis-reduction (ICMR) synthesis of lipophilic tetrapeptides

An efficient, versatile and rapid method toward homologue series of lipophilic tetrapeptide derivatives (herein, the opioid peptides H-TIPP-OH and H-DIPP-OH) is reported. High atom economy and a minimal number of synthetic steps resulted from a one-pot tandem isomerization-cross metathesis-reduction sequence (ICMR), applicable both in solution and solid phase methodology. The broadly applicable synthesis proceeds with short reaction times and simple work-up, as illustrated in this work for alkylated opioid tetrapeptides.

Strategies towards the synthesis of calyciphylline A-type Daphniphyllum alkaloids

The Daphniphyllum alkaloids are a diverse family of natural products rich in number and structural diversity that have been known for many decades. However, the structurally unique subclass of calyciphylline A-type alkaloids has only recently been discovered and is relatively unexplored. Several noteworthy core syntheses and the development of a wide range of novel synthetic strategies have been achieved. This includes strategies based on intramolecular Michael addition, Pd-catalysis, cycloaddition, and Mannich-type reactions. This review will provide an overview of these synthetic studies.