Copper-Catalyzed Coupling of Thioamides and Donor/Acceptor-Substituted Carbenoids: Synthesis of Enamino Esters and Enaminones

The coupling of thioamides and donor/acceptor-substituted diazocarbonyl compounds is reported for the first time. The present report provides a mild, catalytic method that couples thioamides and donor/acceptor-substituted diazocarbonyl compounds to form enamino esters and enaminones. Unlike traditional methods for the synthesis of enamino esters and enaminones from thioamides, both N-alkyl thioamides and thiocarbamates are suitable substrates in this coupling reaction. Copper(I) bromide catalyzes the reaction and provides enamino esters and enaminones chemo- and diastereoselectively in less time than Rh₂(OAc)₄ or Ru(PPh₃)₃Cl₂ catalysts.

Copper(i)-carbenes as key intermediates in the [3 + 2]-cyclization of pyridine derivatives with alkenyldiazoacetates: a computational study

This work reports a computational study of the copper(i)-catalyzed regioselective synthesis of indolizine derivatives through the [3 + 2]-cyclization reaction of vinyldiazo acetates and pyridine derivatives. This reaction is predicted to proceed via a multi-step process with the initial decomposition of the diazo function and generation of an electrophilic copper(i) carbene intermediate. Subsequent attack of the pyridine derivative at the vinylogous position of the carbene would generate a vinylcuprate intermediate that would evolve to the final products through a sequence involving cyclization, reductive elimination, metal decoordination and final oxidative aromatization. According to our calculations, an alternative pathway involving the initial activation of the pyridine seems unlikely. These theoretical results could pave the way for further developments in vinyldiazo chemistry.

α-Thiocarbonyl synthesisviathe FeII-catalyzed insertion reaction of α-diazocarbonyls into S–H bonds

Fe(OTf)₂was used to catalyze the insertion reaction of α-diazocarbonyls into S–H bonds at 40 °C.

Palladium-catalyzed formal insertion of carbenoids into N,O-aminals: direct access to α-alkoxy-β-amino acid esters

A new and efficient reaction has been developed to synthesize α-alkoxy-β-amino acid esters via palladium-catalyzed formal insertion of carbenoids into N,O-aminals.

Application of dialkyl azodicarboxylate frameworks featuring multi-functional properties

The application of dialkyl azodicarboxylates as versatile reagents in Mitsunobu, oxidation, electrophilic, amination and carbonylation reactions is reviewed.

Trifluoromethylation of α-diazoesters and α-diazoketones with fluoroform-derived CuCF3: synergistic effects of co-solvent and pyridine as a promoter

Fluoroform-derived CuCF₃ can efficiently trifluoromethylate α-diazoesters and α-diazoketones. The key is the use of co-solvent and pyridine as a promoter.

A highly diastereoselective [5+1] annulation to 2,2,3-trisubstituted tetrahydroquinoxalines via intramolecular Mannich-type trapping of ammonium ylides

A highly diastereoselective [5+1] annulation to 2,2,3-trisubstituted tetrahydroquinoxalines was developed by us.

Influence of sulfonyl substituents on the decomposition of N-sulfonylhydrazones at room temperature

A systematic investigation on the influence of sulfonyl substituents on the decomposition of N-sulfonylhydrazones at room temperature is described.

3d Transition Metals for C-H Activation

C-H activation has surfaced as an increasingly powerful tool for molecular sciences, with notable applications to material sciences, crop protection, drug discovery, and pharmaceutical industries, among others. Despite major advances, the vast majority of these C-H functionalizations required precious 4d or 5d transition metal catalysts. Given the cost-effective and sustainable nature of earth-abundant first row transition metals, the development of less toxic, inexpensive 3d metal catalysts for C-H activation has gained considerable recent momentum as a significantly more environmentally-benign and economically-attractive alternative. Herein, we provide a comprehensive overview on first row transition metal catalysts for C-H activation until summer 2018.

Metal-Free Insertion Reactions of Diazo Carbonyls to Azlactones

Insertion reactions of diazo carbonyls to azlactones in basic conditions have been performed. The developed method allows the preparation of a wide range of oxazole derivatives in yields ranging from 74 to 98%. Different substituents on both azlactone rings and diazo carbonyls do not compromise the methodology, even those containing stereogenic centers. Isotopic labeling experiments revealed the mechanism may proceed through a rare diazo carbonyl activation by an ammonium salt derivative.

Gold(I)-Catalyzed and H2O-Mediated Carbene Cascade Reaction of Propargyl Diazoacetates: Furan Synthesis and Mechanistic Insights

A novel gold-catalyzed water-mediated carbene cascade reaction of propargyl diazoacetates has been developed. Mechanistic investigation indicates that this reaction is initiated by gold-catalyzed gold-carbene formation followed by an unprecedented 6- endo-dig carbocyclization with tethered alkyne through an oxonium ylide intermediate, terminated by a β-H elimination/protodeauration process to give the aromatized furan products in good to high yields with broad substrate generality. Notably, the proposed gold-carbene intermediates are verified by interception experiments.

Intrinsically Safe and Shelf-Stable Diazo-Transfer Reagent for Fast Synthesis of Diazo Compounds

We report a crystalline compound 2-azido-4,6-dimethoxy-1,3,5-triazine (ADT) as an intrinsically safe, highly efficient, and shelf-stable diazo-transfer reagent. Because the decomposition of ADT is an endothermal process (Δ H = 30.3 kJ mol^-1), ADT is intrinsically nonexplosive, as proved by thermal, friction, and impact tests. The diazo-transfer reaction based on ADT gives diazo compounds in excellent yields within several minutes at room temperature. ADT is very stable upon >1 year storage under air at room temperature.

Regiodivergent Synthesis of Pyrazolines with a Quaternary Carbon Center via Cycloaddition of Diazoesters to N-Purine-Substituted Allenes

Diversity-oriented synthesis of pyrazoline derivatives that contain a quaternary carbon center has been achieved via the 1,3-dipolar cycloaddition between N-purine-substituted allenes and α-alkyl/aryl diazoesters. Using Pd₂(dba)₃ as a catalyst, only 1-pyrazoline derivatives are produced in a regioselective manner. When DPPB is used as a catalyst, diverse 1-pyrazolines and 2-pyrazolines are obtained in moderate to good total yields.

In situ generation of nitrile oxides from copper carbene and tert-butyl nitrite: synthesis of fully substituted isoxazoles

Herein, we present a novel [3 + 2] cycloaddition reaction of β-keto esters with nitrile oxides, which were generated in situ from copper carbene and tert-butyl nitrite. This three-component reaction provides new methodology for the direct synthesis of fully substituted isoxazole derivatives, featuring mild reaction conditions, readily accessible starting materials and simple operation. The experimental studies and DFT calculations suggest that the reaction starts with the generation of the key intermediate nitrile oxides, followed by a [3 + 2] cycloaddition reaction of β-keto esters to give the final isoxazole products.

Two C-O Bond Formations on a Carbenic Carbon: Palladium-Catalyzed Coupling of N-Tosylhydrazones and Benzo-1,2-quinones To Construct Benzodioxoles

A novel and efficient method for the formation of two C-O bonds on a carbenic carbon is reported. This palladium-catalyzed coupling of N-tosylhydrazones and benzo-1,2-quinones were involved the process of carbonyl ylides generation, aromatization, and intramolecular nucleophilic addition, delivering various useful benzodioxoles in high yields.

Iodine-catalyzed diazo activation to access radical reactivity

Transition-metal-catalyzed diazo activation is a classical way to generate metal carbene, which are valuable intermediates in synthetic organic chemistry. An alternative iodine-catalyzed diazo activation is disclosed herein under either photo-initiated or thermal-initiated conditions, which represents an approach to enable carbene radical reactivity. This metal-free diazo activation strategy were successfully applied into olefin cyclopropanation and epoxidation, and applying this method to pyrrole synthesis under thermal-initiated conditions further demonstrates the unique reactivity using this method over typical metal-catalyzed conditions.

The synthesis of pyrroles and oxazoles based on gold α-imino carbene complexes

Cationic gold complexes of α-oximimino carbenes have been identified to react with weak nucleophiles including enol ethers and nitriles. These findings allowed us to develop the highly efficient synthesis of pyrroles and oxazoles.

A copper-catalyzed reaction of 3-diazoindolin-2-imines with 2-(phenylamino)ethanols: convenient access to spiro[indoline-3,2′-oxazolidin]-2-imines

3-Diazoindolin-2-imines reacted with chiral 2-(phenylamino)ethanols under copper catalysis to furnish chiral spiro[indoline-3,2′-oxazolidin]-2-imines in good yields with excellent diastereoselectivity.

Thermally induced N–S bond insertion reaction of diazo compounds with N-sulfenylsuccinimides: synthesis of sulfides and mechanism studies

A metal-free gem-functionalization reaction of diazo compounds via a formal N–S bond insertion process under mild conditions is presented.

A chiral Brønsted acid-catalyzed highly enantioselective Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines

A chiral phosphoric acid-catalyzed asymmetric Mannich-type reaction of α-diazo esters with in situ generated N-acyl ketimines, derived from 3-aryl-3-hydroxyisoindolinones has been demonstrated. The reaction proceeds smoothly under mild reaction conditions.

Transition-Metal-Catalyzed Cross-Couplings through Carbene Migratory Insertion

Transition-metal-catalyzed cross-coupling reactions have been well-established as indispensable tools in modern organic synthesis. One of the major research goals in cross-coupling area is expanding the scope of the coupling partners. In the past decade, diazo compounds (or their precursors N-tosylhydrazones) have emerged as nucleophilic cross-coupling partners in C-C single bond or C═C double bond formations in transition-metal-catalyzed reactions. This type of coupling reaction involves the following general steps. First, the organometallic species is generated by various processes, including oxidative addition, transmetalation, cyclization, C-C bond cleavage, and C-H bond activation. Subsequently, the organometallic species reacts with the diazo substrate to generate metal carbene intermediate, which undergoes rapid migratory insertion to form a C-C bond. The new organometallic species generated from migratory insertion may undergo various transformations. This type of carbene-based coupling has proven to be general: various transition metals including Pd, Cu, Rh, Ni, Co, and Ir are effective catalysts; the scope of the reaction has also been extended to substrates other than diazo compounds; and various cascade processes have also been devised based on the carbene migratory insertion. This review will summarize the achievements made in this field since 2001.

Enantioselective Copper-Catalyzed Oxy-Alkynylation of Diazo Compounds

Enantioselective catalytic methods allowing the addition of both a nucleophile and an electrophile onto diazo compounds give a fast access into important building blocks. Herein, we report the highly enantioselective oxyalkynylation of diazo compounds using ethynylbenziodoxol-(on)e reagents and a simple copper bisoxazoline catalyst. The obtained α-benzoyloxy propargylic esters are useful building blocks, which are difficult to synthesize in enantiopure form using other methods. The obtained products could be efficiently transformed into vicinal diols and α-hydroxy propargylic esters without loss in enantiopurity.