Assembly of 3-sulfonated 2H-pyrrol-2-ones through the insertion of sulfur dioxide with allenoic amides

Generation of 3-sulfonated 2H-pyrrol-2-ones through a three-component reaction of allenoic amides, sulfur dioxide, and aryldiazonium tetrafluoroborates under metal-free conditions is achieved. This transformation proceeds under mild conditions without the addition of catalysts or additives, giving rise to 3-sulfonated 2H-pyrrol-2-ones in moderate to good yields. Good functional group compatibility is observed. A plausible mechanism is proposed, which is initiated by aryl radicals formed in situ from aryldiazonium tetrafluoroborates and DABCO·(SO₂)₂. Additionally, excellent chemoselectivity and regioselectivity are presented in this transformation.     

Generation of Sulfonyl Radicals from Aryldiazonium Tetrafluoroborates and Sulfur Dioxide: The Synthesis of 3‐Sulfonated Coumarins

A catalyst‐free approach for the generation of sulfonyl radicals from aryldiazonium tetrafluoroborates in the presence of DABCO?(SO₂)₂ is realized. The combination of aryldiazonium tetrafluoroborates, DABCO?(SO₂)₂, and aryl propiolates affords 3‐sulfonated coumarins in good to excellent yields. This tandem reaction process involves radical addition, spirocyclization, and 1,2‐migration of esters. Additionally, the in situ diazotization of a number of anilines allows the directional synthesis of desired 3‐sulfonated coumarins in a one‐pot, two‐step process.     

Assembly of 3-sulfonated 2H-pyrrol-2-ones through the insertion of sulfur dioxide with allenoic amides

Generation of 3-sulfonated 2 H-pyrrol-2-ones through a three-component reaction of allenoic amides,sulfur dioxide,and aryldiazonium tetrafluoroborates under metal-free conditions is achieved.This transformation proceeds under mild conditions without the addition of catalysts or additives,giving rise to 3-sulfonated 2 H-pyrrol-2-ones in moderate to good yields.Good functional group compatibility is observed.A plausible mechanism is proposed,which is initiated by aryl radicals formed in situ from ...     

Synthesis of aryl allylic fluorides by direct electrophilic fluorination of alkenes

Aryl allylic fluorides were synthesized in 47-83% yields by using Selectfluor as the electrophilic reagent in DMF. The outcome of this reaction may be explained by electronic effects while the reactivity was controlled by the stabilization effect of the aryl group on the benzylic cationic intermediates.     

Metal‐Free Aminosulfonylation of Aryldiazonium Tetrafluoroborates with DABCO⋅(SO2)2 and Hydrazines

The coupling of aryldiazonium tetrafluoroborates, DABCO?(SO₂)₂, and hydrazines under metal‐free conditions leads to the formation of aryl N‐aminosulfonamides. The reaction proceeds smoothly at room temperature and shows broad functional‐group tolerance. A radical process is proposed for this transformation.     

Chiral Anion Phase Transfer of Aryldiazonium Cations: An Enantioselective Synthesis of C3‐Diazenated Pyrroloindolines

Herein is reported the first asymmetric utilization of aryldiazonium cations as a source of electrophilic nitrogen. This is achieved through a chiral anion phase‐transfer pyrroloindolinization reaction that forms C3‐diazenated pyrroloindolines from simple tryptamines and aryldiazonium tetrafluoroborates. The title compounds are obtained in up to 99 % yield and 96 % ee. The air‐ and water‐tolerant reaction allows electronic and steric diversity of the aryldiazonium electrophile and the tryptamine core.     

Electrochemical Arylation of Electron‐Deficient Arenes through Reductive Activation

An electrochemical method has been developed to achieve arylation of electron‐deficient arenes through reductive activation. Various electron‐deficient arenes and aryldiazonium tetrafluoroborates are amenable to this transformation within the conditions of an undivided cell, providing the desired products in up to 92 % yield. Instead of preparing diazonium reagents, these reactions can begin from anilines, and they can be carried out in one pot. Electron paramagnetic resonance studies indicate that cathodic reduction of quinoxaline occurs using the transformation. Moreover, cyclic voltammetry indicates that both quinoxaline and aryl diazonium salt have relatively low reduction potentials, which suggests they can be activated through reduction during the reaction.     

Enantioselective fluorination mediated by cinchona alkaloid derivatives/Selectfluor combinations: reaction scope and structural information for N-fluorocinchona alkaloids.

Cinchona-alkaloid/Selectfluor combinations efficiently fluorinate a variety of carbonyl compounds in a highly enantioselective manner to furnish chiral alpha-fluorocarbonyl compounds. The DHQB/Selectfluor combination is effective for the enantioselective fluorination of indanones and tetralones 1 in up to 91% ee. The first enantioselective syntheses of chiral derivatizing reagents 3 was accomplished with high ee and in high chemical yields by the DHQDA/Selectfluor combination. 3-Fluorooxindoles 7 were prepared with ee up to 83% using the (DHQ)2AQN/Selectfluor or the (DHQD)2PYR/Selectfluor combination. Since the combinations are conveniently prepared in situ from readily available reagents, the present system represents a practical method for enantioselective fluorination. X-ray crystallography and 1H NMR analyses of the cinchona alkaloids/Selectfluor combination have established that the species that mediate this novel reaction are N-fluoroammonium cinchona alkaloid tetrafluoroborates, which adopt open conformations.     

Synthesis of aryl fluorides by decomposition of aryldiazonium hexafluorogermanates

Conclusions Seven aryldiazonium hexafluorogermanates have been synthesized, and the corresponding aryl fluorides have been prepared from them in 60–75% yield, by thermal decomposition.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 12, pp. 2750–2752, December, 1967.     

Efficient synthesis of 3-arylbutadiene sulfones using the Heck–Matsuda reaction

An efficient and practical method for a scalable synthesis of 3-arylbutadiene sulfones deals with the ligand-free Heck–Matsuda reaction of sulfolene with aryldiazonium tetrafluoroborates followed by triethylamine-promoted double bond shift.     

Intermolecular Radical Carbofluorination of Non‐activated Alkenes

The Meerwein arylation has recently become an even more powerful tool for the functionalization of alkenes. Besides the attachment of an aryl group, radical reactions of this type allow the introduction of several different heteroatoms and a broad variety of alkenes are meanwhile tolerated as substrates. Closing a long‐standing gap of the methodology, this communication describes the first intermolecular Meerwein‐type carbofluorination. In metal‐free reactions, arylalkyl fluorides were obtained from arylhydrazines and alkenes with Selectfluor acting as oxidant and as radical fluorine source.     

Some studies on the photo-initiated cationic polymerisation of epoxides

Several triarylsulphonium and diaryliodonium compounds have been synthesised. Alkylarylsulphonium compounds were obtained by alkylating diaryl sulphides with trialkyloxonium salts and by reaction of diaryl sulphides with alkyl halides in the presence of silver tetrafluoroborate. Photolysis of the sulphonium salts in methanol gave diaryl sulphides and, in the case of triarylsulphonium compounds, the appropriate aromatic hydrocarbon and its methyl ether. Diaryliodonium tetrafluoroborates and pentafluorophosphates gave aryl fluorides, biaryls and aromatic hydrocarbons. The decomposition of the salts is suggested as occurring via both free radical and ionic pathways. The ability of the compounds to sensitise the polymerisation of epoxy resins was found to be dependent upon the counterion (hexafluorophosphates being more efficient than tetrafluoroborates) and upon the structure of the cation. Sensitised cationic initiated polymerisation was also investigated and it was found that both excited singlet state and triplet state sensitisers were effective.     

Synthesis of β‐Keto Sulfones by a Catalyst‐Free Reaction of Aryldiazonium Tetrafluoroborates,Sulfur Dioxide,and Silyl Enol Ethers

A green approach for the generation of β‐keto sulfones through a reaction of aryldiazonium tetrafluoroborates and sulfur dioxide with silyl enol ether under catalyst‐ and additive‐free conditions has been realized. This reaction proceeds efficiently at room temperature and goes to completion in half an hour. During the reaction process, aryldiazonium tetrafluoroborate is treated with DABCO ⋅ (SO₂)₂ (DABCO=1,4‐diazabicyclo[2.2.2]octane) to provide a sulfonyl radical as the key intermediate, which then initiates the transformation. Oxidants or metal catalysts are avoided, and the presence of DABCO also plays an important role in the reaction.     

Copper-mediated fluorination of aryl iodides

The synthesis of aryl fluorides has been studied intensively because of the importance of aryl fluorides in pharmaceuticals, agrochemicals, and materials. The stability, reactivity, and biological properties of aryl fluorides can be distinct from those of the corresponding arenes. Methods for the synthesis of aryl fluorides, however, are limited. We report the conversion of a diverse set of aryl iodides to the corresponding aryl fluorides. This reaction occurs with a cationic copper reagent and silver fluoride. Preliminary results suggest this reaction is enabled by a facile reductive elimination from a cationic arylcopper(III) fluoride.     

Additions to N‐Sulfinylamines as an Approach for the Metal‐free Synthesis of Sulfonimidamides: O‐Benzotriazolyl Sulfonimidates as Activated Intermediates

Sulfonimidamides are obtained in moderate to very good yields from the key intermediates O‐benzotriazolyl sulfonimidates, which are formed by reacting aryldiazonium tetrafluoroborates, N‐tritylsulfinylamine, and N‐hydroxybenzotriazole hydrate in a process mediated by a tertiary amine. The formation of the sulfonimidate proceeds in inexpensive and environmentally benign dimethyl carbonate as the solvent, it does not require anhydrous conditions, and the product yields generally exceed 70 %. The substrate scope is broad, and a wide range of sensitive organic functionalities is well tolerated. The reactions probably proceed via aryl radicals formed from diazonium cations with assistance from both the tertiary amine and the sulfinylamine.     

Trifluoromethylselenolation of Aryldiazonium Salts: A Mild and Convenient Copper‐Catalyzed Procedure for the Introduction of the SeCF3 Group

The straightforward introduction of the trifluoromethylseleno group into aromatic and heteroaromatic compounds is accomplished by the utilization of readily available aryldiazonium tetrafluoroborates, potassium selenocyanate, and Ruppert–Prakash reagent. The reaction tolerates a wide range of aromatic and heteroaromatic diazonium salts and is also amenable to the synthesis of pentafluoroethyl selenoethers. Furthermore, the methodology can be applied directly starting from anilines.     

Sequential cross-metathesis/electrophilic fluorodesilylation: a novel entry to functionalized allylic fluorides

Various allylic fluorides were prepared using a two-step process involving a cross-metathesis of allyltrimethylsilane with different olefinic partners followed by a fluorodesilylation of the corresponding functionalized allylsilanes with Selectfluor. [reaction: see text]     

The standard redox potential of the phenyl radical/anion couple

The voltammogram of aryldiazonium tetrafluoroborates in acetonitrile (ACN), at low concentration, shows a first one-electron wave followed at a more negative potential by a small second wave; this last one corresponds to the reduction of the radical formed at the level of the first wave. Simulation of the voltammogram permits one to determine the standard redox potential of the radical/anion couple Eo(Ph./Ph-) = 0.05 V/SCE and the reduction mechanism of the diazonium cation. An electron transfer concerted with the cleavage of the C-N bond furnishes the aryl radical; this radical undergoes two competitive reactions: reduction at the electrode and H-atom transfer.     

Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes,Aryldiazonium Salts,and Aldehydes

A highly selective multicomponent carbonyl allylation reaction of 1,3‐butadienes, aryldiazonium tetrafluoroborates, and aldehydes has been established under the combined catalysis of palladium acetate and chiral anion phase transfer to render the favorable assembly of chiral Z‐configured homoallylic alcohols in high yields and with excellent levels of enantioselectivity.     

Catalytic Enantioselective Assembly of Homoallylic Alcohols from Dienes,Aryldiazonium Salts,and Aldehydes

A highly selective multicomponent carbonyl allylation reaction of 1,3‐butadienes, aryldiazonium tetrafluoroborates, and aldehydes has been established under the combined catalysis of palladium acetate and chiral anion phase transfer to render the favorable assembly of chiral Z‐configured homoallylic alcohols in high yields and with excellent levels of enantioselectivity.