Functionalization of Diazo Groups by the Nucleophilic Addition of Two Molecules of a Dimethylsulfonium Ylide to α-Diazo-β-ketoesters/ketones: Synthesis of Highly Functionalized Hydrazones

Direct synthesis of enone-hydrazones under solvent free and additive free conditions

A series of enone-hydrazones were synthesized through the reaction of enaminones with hydrazones under solvent-free, additive-free, and metal-catalyst-free conditions. The target products were obtained in high yields, with outstanding group tolerance, stereoselectivity, and chemical selectivity. In this work, a series of novel enaminone skeleton compounds were synthesized, and deuteration experiments showed that enone-hydrazones have different properties from traditional electron-deficient enketones.

Tunable electrochemical diverse sulfurization of sulfoxonium ylides with disulfides

An electrochemical protocol for the synthesis of sulfursulfoxonium ylides and 1,3-dithioketals by reacting sulfoxonium ylides with disulfides has been developed under simple and mild conditions. By changing the solubility of the raw materials and the dielectric parameters of the electrolyte, sulfurization enabled a selective dehydrogenation of C-S and the construction of 1,3-dithioketals. The transformation is an ideal approach to prepare organosulfur reagents with a broad functional group tolerance as well as high selectivity, which leads to vicinal difunctionalized organosulfur compounds.

DBU-Promoted Tandem Cyclization of Ynones and Diazo Compounds: Direct Synthesis of Eight-Membered Cyclic Ethers

A novel DBU-promoted tandem cyclization reaction of ynones with diazo compounds as the N-terminal electrophiles has been developed. The reaction provides a simple and efficient method for the synthesis of fused eight-membered oxocino[2,3-c] pyrazoles from readily available acyclic starting materials in a single step. This reaction allows the formation of four new bonds and two rings in a highly regio- and diastereoselective manner, where two adjacent stereocenters are created simultaneously in an atom-economic manner.

Quantification of the Electrophilicities of Diazoalkanes: Kinetics and Mechanism of Azo Couplings with Enamines and Sulfonium Ylides

Kinetics and mechanism of the reactions of methyl diazoacetate, dimethyl diazomalonate, 4-nitrophenyldiazomethane, and diphenyldiazomethane with sulfonium ylides and enamines were investigated by UV-Vis and NMR spectroscopy. Ordinary alkenes undergo 1,3-dipolar cycloadditions with these diazo compounds. In contrast, sulfonium ylides and enamines attack at the terminal nitrogen of the diazo alkanes to give zwitterions, which undergo various subsequent reactions. As only one new bond is formed in the rate-determining step of these reactions, the correlation lg k₂ (20 °C)=s_N (N+E) could be used to determine the one-bond electrophilicities E of the diazo compounds from the measured second-order rate constants and the known reactivity indices N and s_N of the sulfonium ylides and enamines. The resulting electrophilicity parameters (-21<E<-18), which are 11-14 orders of magnitude smaller than that of the benzenediazonium ion, are used to define the scope of one-bond nucleophiles which may react with these diazoalkanes.

Synthesis of 4-trifluoromethyl pyridazines via annulation of pyridinium ylides with trifluoroacetyl diazoester

A base promoted annulation of pyridinium ylides with trifluoroacetyl diazoester has been reported. Highly functionalized 4-trifluoromethyl pyridazines were synthesized in good yields without the use of any heavy metal catalysts. The developed methodology was compatible with a variety of important functional groups. Mechanistic studies revealed that trifluoroacetylated hydrazone was an active intermediate of this three-component annulation. Synthetic versatility of the method via aminolysis and condensation toward amide- and pyridazino[4,5-c]pyridazine-derivatives has been showcased.

Formal (3 + 1 + 1) Carboannulation of Morita-Baylis-Hillman Carbonates with Pyridinium Ylides: Access to Spiro-Cyclopentadiene Oxindoles

An efficient formal (3 + 1 + 1) carboannulation strategy of Morita-Baylis-Hillman (MBH) carbonates with pyridinium ylides was developed for constructing diversely functionalized spiro-cyclopentadiene oxindoles. The reaction initiates with an S_N2' olefination of MBH carbonates with pyridinium ylides. The in situ generated dienes then engage in a challenging (4 + 1) ylide carboannulation, which has been rarely reported before. The reaction features broad substrate scope as well as high chemo- and regioselectivity. (3 + 1 + 1) carboannulation products could be easily transformed into interesting spiro-cyclopenta[c]furan oxindoles.

Multicomponent Reactions Involving Diazo Reagents: A 5-Year Update

This review summarizes recent developments in multicomponent reactions of diazo compounds. The role of diazo reagent and the type of interaction between components was analyzed to structure the discussion. In contrast to previous reviews on related topics mostly focused on metal catalyzed transformations, a substantial amount of organocatalytic or catalyst-free methodologies is covered in this work.

Gold-Catalyzed Synthesis of Diaza-hexatrienes Via Diazo Attack at Vinylgold Carbenes: An Easy Access to 1H-Pyrazolo[4,3-b]pyridine-5-ones

This work reports a gold-catalyzed stereoselective synthesis of highly substituted E-configured 2,3-diaza-1,3,5-hexatrienes using α-diazo nitriles and cyclopropene derivatives; such products arise from an atypical diazo attack of α-aryldiazo nitriles at vinylgold carbenes. For these 2,3-diaza-1,3,5-hexatrienes, we develop a novel anionic cyclization of derivatives of one family to form 1H-pyrazolo[4,3-b]pyridine-5-ones.

(2 + 1 + 1 + 1)-Annulation Reactions of Aryldiazonium Tetrafluoroborates with Sulfur Ylides to Polysubstituted Pyrazoles

Novel divergent domino annulation reactions of sulfur ylides with aryldiazonium tetrafluoroborates have been developed, affording various tetra- and trisubstituted pyrazole derivatives in moderate to good yields. Three molecules of sulfur ylides were applied as C1 synthon to construct the complex products with five new chemical bonds formed in these one-pot reactions.

Base Promoted Three-Component Annulation of 4-Diazoisochroman-3-imines with Dimethylsulfonium Ylides: Synthesis of Highly Functionalized Isochromeno[4,3-c]pyridazines

A novel method has been developed to synthesize a unique class of highly functionalized isochromeno[4,3-c]pyridazines. This reaction features an intermolecular functionalization of terminal nitrogen atom of diazo group of 4-diazoisochoman-3-imine with two dimethylsulfonium ylide components, followed by a base promoted 6-exo-trig cyclization step. Readily available starting materials, a broad substrate scope, and operationally simple, mild, and catalyst-free reaction conditions are the prominent features of this method.

Metal-Free Chemoselective Reaction of Sulfoxonium Ylides and Thiosulfonates: Diverse Synthesis of 1,4-Diketones, Aryl Sulfursulfoxonium Ylides, and β-Keto Thiosulfones Derivatives

A diverse chemoselective insertion reaction of sulfoxonium ylides and thiosulfonates under transition-metal-free conditions is developed, which successfully affords 1,4-diketone compounds, arylthiosulfoxide-ylides, and β-keto thiosulfones, respectively. The nucleophilic addition of two molecular sulfoxonium ylides to construct sulfone-substituted 1,4-dione compounds is the highlight of this work.