C(sp3)-H Alkenylation of Tetrahydroisoquinolines via Merging Electrochemistry and Organocatalysis

C(sp³)-H alkenylation of tetrahydroisoquinoline by merging Shono oxidation and the Morita-Baylis-Hillman reaction is developed, employing 4-dimethylaminopyridine as an organocatalyst and TEMPO/NaBr as an electrocatalyst. The reaction proceeds via the interception of an iminium cation intermediate, which is generated in situ from anodic oxidation, leading to aza-Morita-Baylis-Hillman reaction products. Additionally, the use of TEMPO and NaBr as mediators is crucial to avoid the decomposition of products by lowering the oxidation potential of the reaction.

TEMPO-Enabled Electrochemical Enantioselective Oxidative Coupling of Secondary Acyclic Amines with Ketones

An electrochemical asymmetric coupling of secondary acyclic amines with ketones via a Shono-type oxidation has been described, affording the corresponding amino acid derivatives with good to excellent diastereoselectivity and enantioselectivity. The addition of an N-oxyl radical as a redox mediator could selectively oxidize the substrate rather than the product, although their oxidation potential difference is subtle (about 13 mV). This electrochemical transformation proceeds in the absence of stoichiometric additives, including metals, oxidants, and electrolytes, which gives it good functional group compatibility. Mechanistic studies suggest that proton-mediated racemization of the product is prevented by the reduction of protons at the cathode.

Electrochemical asymmetric synthesis of biologically active substances

Electrically driven oxidation and reduction reactions are well-established methods for synthesis even in the chemical industry, but asymmetric versions are still few. The mild conditions used, atom efficiency and low cost make these reactions a very attractive alternative to other methods of synthesis. Very fine tuning can be achieved based on minute changes in potentials, allowing only one functional group in a molecule to react in the presence of several others, which is ideal for applications in total synthesis. In this review, the literature in the field of asymmetric synthesis of biologically active substances over the last 10 years is surveyed.

Direct access to vicinally functionalized and N-trifluoroacetylated (bicyclic)ketopiperazines using a readily affordable N-heterocyclic anhydride

Functionalized 2-piperazinones play essential roles as conformationally-constrained peptidomimetics by mimicking inverse γ-turns in peptides. Here, we describe an efficient, scalable, stereoselective, modular, and chemoselective annulation protocol between a novel N-trifluoroacetyl anhydride and several reactive partners, including lactim ethers, imidoyl chlorides, aryl aldimines, and 1,3-azadienes, leading to vicinally functionalized (bicyclic) 2-piperazinones.

Anodic Oxidation for the Stereoselective Synthesis of Heterocycles

Stereodefined aliphatic heterocycles are one of the fundamental structural motifs observed in natural products and biologically active compounds. Various strategies for the synthesis of these building blocks based on transition metal catalysis, organocatalysis, and noncatalytic conditions have been developed. Although electrosynthesis has also been utilized for the functionalization of aliphatic heterocycles, stereoselective transformations under electrochemical conditions are still a challenging field in electroorganic chemistry. This Account consists of four main topics related to our recent efforts on the diastereo- and/or enantioselective synthesis of aliphatic heterocycles, especially N-heterocycles, using anodic oxidations as key steps. The first topic is the development of stereoselective synthetic methods for multisubstituted piperidines and pyrrolidines from anodically prepared α-methoxy cyclic amines. Our strategies were based primarily on N-acyliminium ion chemistry, and the key electrochemical transformations were diastereoselective anodic methoxylation, diastereoselective arylation, and anodic deallylative methoxylation. Furthermore, we found a unique property of the N-cyano protecting group that enabled the electrochemical α-methoxylation of α-substituted cyclic amines. The second topic of investigation is memory of chirality in electrochemical decarboxylative methoxylation. We observed that the electrochemical decarboxylative methoxylation of oxazolidine and thiazolidine derivatives with the appropriate N-protecting group occurred in a stereospecific manner even though the reaction proceeded through an sp² planar carbon center. Our findings demonstrated the first example of memory of chirality in N-acyliminium ion chemistry. The third topic is the synthesis of chiral azabicyclo-N-oxyls and their application to chiral organocatalysis in the electrochemical oxidative kinetic resolution of secondary alcohols. The final topic is stereoselective transformations utilizing anodically generated halogen cations. We investigated the oxidative kinetic resolution of amino alcohol derivatives using anodically generated bromo cations. We also developed an intramolecular C-C bond formation of keto amides, a diastereoselective bromoiminolactonization of α-allyl malonamides, and an oxidative ring expansion reaction of allyl alcohols. It is noteworthy that most of the electrochemical reactions were performed in undivided cells under constant-current conditions, which avoided a complicated reaction setup and was beneficial for a large-scale reaction. In addition, we developed some enantioselective electrochemical transformations that are still challenges in electroorganic chemistry. We hope that our research will contribute to the further development of diastereo- and/or enantioselective transformations and the construction of valuable heterocyclic compounds using an electrochemical approach.

Copper-catalyzed alkenylation of novel N-iodoarylated allylic ketopiperazinonates with unactivated alkenes

Novel N-iodoarylated allylic ketopiperazines have been engaged in a CuBr-catalyzed alkenylation protocol with simple alkenes, leading to epimerization-free, efficient, and regioselective synthesis of N-stilbeno-ketopiperazines

Iridium-catalyzed α-alkynylation of cyclic nonaromatic eneformamides: application to the synthesis of azapolycyclic architectures

A regioselective and chelation-assisted dehydrogenative alkynylation of cyclic nonaromatic eneformamides with terminal alkynes, under iridium catalysis, is described.

Synthetic Organic Electrochemical Methods Since 2000: On the Verge of a Renaissance

Electrochemistry represents one of the most intimate ways of interacting with molecules. This review discusses advances in synthetic organic electrochemistry since 2000. Enabling methods and synthetic applications are analyzed alongside innate advantages as well as future challenges of electroorganic chemistry.

Regiocontrolled synthesis of (hetero)aryl and alkenyl dehydropyrrolidines, dehydropiperidines and azepenes by Ru-catalyzed, heteroatom-directed α-C–H activation/cross-coupling of cyclic enamides with boronic acids

The synthesis of α-aryl and alkenyl pyrrolidine-, piperidine-, and azepane derivatives by ruthenium-catalyzed, carbonyl-assisted, site-selective sp² C–H activation of cyclic enamides and concomitant cross-coupling with boronic acids is described.

One-shot access to α,β-difunctionalized azepenes and dehydropiperidines by reductive cross-coupling of α-selenonyl-β-selenyl enamides with organic bromides

The synthesis of α- and α,β-functionalized azepenes and dehydropiperidines from readily prepared α-selenonyl eneformamides or enecarbamates has been achieved through Fe-catalyzed α-substitutive deselenonation, β-regioselective lithiation/trapping, and Co-catalyzed reductive cross-coupling protocols.

A practical anodic oxidation of aminofurazans to azofurazans: an environmentally friendly route

Nickel oxyhydroxide anode is effective green tools for the electrooxidation of aminofurazans to azofurazans inca. 1% aqueous NaOH at 20 °C. The reaction is simple and convenient, eliminating the use of expensive and toxic organic or inorganic oxidants.

Expedient access to α,β-difunctionalized azepenes using α-halo eneformamides: application to the one-pot synthesis of 2-benzazepanes

The regioselective synthesis of α,β-difunctionalized (alkenyl, aryl, sulfonyl, allyl, or alkynyl) azepenes has been accomplished through α-halo eneformamides.

Direct access to functionalized azepanes by cross-coupling with α-halo eneformamides

The synthesis of functionalized azepanes was accomplished through the palladium-mediated cross-coupling of α-halo eneformamides with mostly unactivated nucleophiles under mild conditions. Alkenylations proceeded with excellent stereoselectivitiy. In most cases, high yields of the coupling products were obtained.