Merging Electrochemical Synthesis and Post-Ugi Cyclization for the Synthesis of Diverse 4-Imidazolidinones.

Despite the appreciation for electro-organic synthesis, postmulticomponent reaction transformation chemistry rarely exploits this powerful technology. Herein, we explore post-Ugi cyclization reactions using N-centered radical-mediated intramolecular ipso cyclization to synthesize diverse spirocyclic variants of 4-imidazolidinones through the use of electrochemically generated amidyl radicals from the bis-amides of the Ugi adducts. This protocol features an undivided cell setup under constant-current conditions with carbon-platinum electrodes. These metal- and reagent-free reactions are scalable and have broad substrate scope.

Electrochemical Post-Ugi Cyclization for the Synthesis of Highly Functionalized Spirolactams.

The combination of the Ugi reaction and electro-organic synthesis can aid in the creation of novel heterocycles that have not been previously explored. In this study, a new strategy utilizing bis-amides from the Ugi reaction has been developed, which can produce C-S, C-Se, and C-C═O functionalized five-membered spirolactams mediated by electricity under catalyst- and metal-free conditions. Notably, this approach can be applied using a microelectro-flow reactor (µ-EFR) for gram-scale synthesis. The described strategy can synthesize complex azaspiro-fused tricyclic scaffolds with high diastereo- and regioselectivity, highlighting its versatility and potential.

Electro-Oxidative sp3 C-H Bond Functionalization and Annulation Cascade: Synthesis of Novel Heterocyclic Substituted Indolizines.

Indolizine derivatives are prevalent in many synthetic intermediates, pharmaceuticals, and organic materials. Herein, we report a novel electro-oxidative cascade cyclization reaction that uses electricity as the primary energy input to promote the reaction, leading to a series of heterocyclic substituted indolizine derivatives under exogenous-oxidant-free conditions. It is noteworthy that this electrochemical method provides a novel strategy for generating heterocyclic diversity of quinazolinones and quinolines on indolizines. In addition, the sole byproduct in the reaction was molecular hydrogen.

Electrochemical Regioselective Sulfenylation of 2H-Indazoles with Thiols in Batch and Continuous Flow.

A novel electrochemical cross-dehydrogenative C-S bond coupling of aryl thiols with 2H-indazole is reported. Thiol-functionalized 2H-indazoles were synthesized under catalyst-, oxidant-, and metal-free conditions with innocuous hydrogen as the sole byproduct at ambient temperature. Furthermore, continuous electrochemical flow conditions using a graphite/Ni flow cell were used to obtained 3-(arylthio)-2H-indazole compounds on a gram scale within the residence time of 39 min. Detailed mechanistic studies including control experiments and cyclic voltammetry are provided to support the radical-radical cross-coupling pathway.

Electrochemical metal- and oxidant-free synthesis of S-thiocarbamates.

An expeditious synthetic strategy to access functionalized S-thiocarbamates was developed in good to excellent yields and with high current efficiencies. Readily available isocyanides and thiols were used as the starting materials under simple metal- and oxidant-free reaction conditions avoiding an inert atmosphere. The practical application of the present methodology was achieved by electrochemical synthesis of the herbicides prosulfocarb and pebulate. Furthermore, continuous electrochemical flow conditions using a graphite/Pt flow cell were used to obtain S-thiocarbamate compounds on a gram scale within a residence time of 35 min.

Catalyst-Controlled Structural Divergence: Selective Intramolecular 7-endo-dig and 6-exo-dig Post-Ugi Cyclization for the Synthesis of Benzoxazepinones and Benzoxazinones.

Metal catalyzed post-Ugi cyclization of bis-amides is reported in this study. Exposure of bis-amides to Pd(II) catalyst triggered the formation of seven-membered benzoxazepinones. This investigation established that changing the catalyst to a Echavarren's gold(I) turned off cyclization to seven member ring and turned on 6-exo-dig annulations to afford family of six-membered benzoxazinones. To support the proposed mechanisms, quantum chemical based density functional theory calculations have been performed and validated. This novel method obtained molecular complexity up to four modular inputs and divergence of two different skeletons. 2D NMR spectroscopic techniques and single crystal X-ray diffraction established the proposed structures.

Electrochemical Synthesis of Carbodiimides via Metal/Oxidant-Free Oxidative Cross-Coupling of Amines and Isocyanides.

This work discloses an electrochemical oxidative cross-coupling of amines with aryl and aliphatic isocyanides. In an undivided cell, the reaction proceeds without involving any transition-metal catalyst, oxidant, or toxic reagents providing carbodiimides in good yields, thereby circumventing stoichiometric chemical oxidants, with H2 as the only byproduct. Moreover, carbodiimides were in situ converted into unsymmetrical ureas in moderate to good yields using an electricity ON-OFF strategy.

Phenanthridine-Fused Tetracyclic Ring System: Metal-Free Diastereoselective Modular Construction of Highly Constrained Polyheterocycles via Post-Ugi Tandem Modifications.

A metal-free diastereo-/regioselective modular synthetic approach for the synthesis of highly constrained tetrahydroquinoline-fused tetracyclic heterocycles from easily available substrates has been developed. This two-step strategy utilizes an Ugi four-component reaction, followed by the intramolecular spirocarbocyclization and iodination reactions in a single operation. The transformation is mild and operationally simple, which provides architecturally complex polycyclic heterocycles with high diastereoselectivity. Furthermore, the preliminary cytotoxicity screening of selected compounds displayed promising anticancer activity against human cancer cell lines.

Catalyst- and Solvent-Free Coupling of 2-Methyl Quinazolinones and Isatins: An Environmentally Benign Access of Diastereoselective Schizocommunin Analogues.

An environmentally benign highly atom-economic protocol for the construction of the C-C bond has been developed under catalyst- and solvent-free conditions. This protocol involves the efficient coupling of 2-methyl quinazolinones with isatin for the highly diastereoselective access of schizocommunin derivatives in excellent yields (up to 97%). Furthermore, the preliminary cytotoxicity screening of selected schizocommunin analogues displayed promising anticancer activity against human cancer cell lines, and the cytotoxic potential of active compound 12ac was also validated by in silico molecular docking simulation studies.