Cationic arylation through photo(sensitised) decomposition of diazonium salts. Chemoselectivity of triplet phenyl cations

The photodediazoniation of some 4-X-phenyldiazonium tetrafluoborates in MeCN leads to the singlet phenyl cations (X = H, tert-butyl, NMe2, CN), which add to the solvent yielding the corresponding acetanilides. Triplet sensitisation, however, leads to the triplet phenyl cation, which is reduced in neat solvent and is trapped by pi nucleophiles (allyltrimethylsilane and benzene), resulting in an ionic analogue of the Meerwein or Gomberg arylations. With the 4-nitro derivative intersystem crossing prevails over dediazoniation from the singlet and with the 4-cyano competes with it, so that in those cases the triplet phenyl cation is formed also upon direct irradiation.     

Hydroperoxides and aryl diazonium salts as reagents for the functionalization of non-activated olefins

Hydroperoxides, olefins, and arenediazonium salts selectively combine to give azo compounds via an iron(II)-mediated three-component reaction. Starting with a fragmentation liberating acetic acid, the hydroperoxides act as radical source and the diazonium ions as nitrogen-centered radical scavengers.     

Electrophilic substitution of diazonium salts in 2-amino-4-(alkyl or aryl)oxazoles

Aryl diazonium fluoborates react readily with 2-amino-4-alkyloxazoles and 2-amino-4-aryloxazoles under mild conditions. The products are the corresponding 5-arylazo derivatives formed, in 44-98% yield free from side products.     

A fast and efficient method for the preparation of aryl azides using stable aryl diazonium silica sulfates under mild conditions

An efficient, fast, and straightforward procedure for the synthesis of aromatic azides using aryl diazonium silica sulfates and sodium azide at room temperature under mild conditions is described. The use of inexpensive materials, simple and clean work-up, short reaction times and good yields are advantages of this method.     

Influence of free and copolymerized triplet quenchers on the photolysis of poly(vinyl phenyl ketone) in solution

The influence of free, diffusion-control quenchers of triplets (naphthalene, biphenyl, 2,5-dimethyl-2,4-hexadiene) on the photolysis of poly(vinyl phenyl ketone) in benzene solution has been investigated. The Stern-Volmer plots for quenching of main-chain scission were linear, and the quenching constants were independent of the macroviscosity of the solutions. Copolymers of vinyl phenyl ketone with 1-vinylnaphthalene and 2-vinylnaphthalene containing as much as 10% (by weight) vinylnaphthalene were prepared. The photolysis of the copolymers was compared with the photolysis of poly(vinyl phenyl ketone) in the presence of free naphthalene. It was found that the quenching efficiency of found naphthalene units was about 21 times higher. The possibility of migration of the absorbed energy along the polymer chain is discussed. The relation between average-number molecular weight M _n and intrinsic viscosity [η] has been determined osmometrically. For unfractionated poly(vinyl phenyl ketone) in benzene at 30°C, the relation [η] = 2.82 × 10^?5 M _n^0.84 has been found.     

A mild and general method for the synthesis of 5-substituted and 5,5-disubstituted fulleroprolines

The reductive ring-opening of fullerenyldihydropyrrole yields ethyl N-benzhydryl fullerenyl[60]glycinate, which is deprotected to give ethyl fullerenylglycinate. The free amine is able to react with a variety of aldehydes and ketones in a Mannich-type process to produce 5-substituted and 5,5-disubstituted fulleroprolines and represents a versatile and general strategy to this class of compounds.     

Probing for a leaving group effect on the generation and reactivity of phenyl cations

Phenyl cations are smoothly generated by the photoheterolytic cleavage of an Ar-LG bond (LG = leaving group). With the aim of evaluating the scope of the method, a series of 4-methoxy-2-(trimethylsilyl)phenyl derivatives (sulfonic, LG = MeSO(3) and CF(3)SO(3), phosphate, LG = (EtO)(2)(O)PO esters and the corresponding chloride) have been compared as probes for evaluating the leaving group ability. The photocleavage was a general reaction, with the somewhat surprising order (EtO)(2)(O)PO ～ Cl > CF(3)SO(3) > MeSO(3) (Φ = 0.50 to 0.16 in CF(3)CH(2)OH and lower values in MeCN-H(2)O). The ensuing reactions did not depend on the LGs but only on the structure of the phenyl cation (the silyl group tuned the triplet to singlet intersystem crossing and the electrophilicity) and on the medium (formation of a complex with water slowed the electrophilic reactions).     

The Mg-oppenauer oxidation as a mild method for the synthesis of aryl and metallocenyl ketones

Magnesium alkoxides undergo a hydride-transfer oxidation with benzaldehyde as the oxidant. This magnesium variant of the Oppenauer oxidation was used for the synthesis of polyfunctional biaryl ketones. LiCl was found to promote this reaction by enhancing the solubility of magnesium alkoxides. This mild oxidation method was especially useful for preparing ketones bearing a metallocenyl unit as well as various new ferrocenyl ketones and tricarbonylchromium complexes. This last class of ketones was reduced with the CBS catalyst (CBS=Corey-Bakshi-Shibata, diphenyl oxazaborolidine) to chiral benzhydrol complexes with high enantioselectivity enabling an asymmetric synthesis of electron-rich or -poor benzhydryl alcohols (up to 94 % ee).     

Pd/P(t-Bu)(3): a mild and general catalyst for Stille reactions of aryl chlorides and aryl bromides

Pd/P(t-Bu)(3) serves as an unusually reactive catalyst for Stille reactions of aryl chlorides and bromides, providing solutions to a number of long-standing challenges. An unprecedented array of aryl chlorides can be cross-coupled with a range of organotin reagents, including SnBu(4). Very hindered biaryls (e.g., tetra-ortho-substituted) can be synthesized, and aryl chlorides can be coupled in the presence of aryl triflates. The method is user-friendly, since a commercially available complex, Pd(P(t-Bu)(3))(2), is effective. Pd/P(t-Bu)(3) also functions as an active catalyst for Stille reactions of aryl bromides, furnishing the first general method for room-temperature cross-couplings.     

UV photolysis of protonated ruthenium and osmium decamethylmetallocenes as a new method for synthesis of the metallonium cations

Decamethylmetallocenes Cp^* ₂M (M=Ru, Os) in the presence, of acids (CF₃CO₂H, CF₃SO₃H) give thepprotonation products [Cp^* ₂MH]⁺An⁻. Broad-band UV photolysis of their solutions results in the formation of the salts of onium cations . A preparative procedure for the synthesis of these salts has been developed. Hydrolysis of the salts gives the carbinol Cp^*MC₅Me₄CH₂OH. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 587–591. March, 1999.     

Synthesis and photochemistry of novel bromo substituted stilbene derivatives as triplet state sensitizers for the generation of singlet oxygen

We have presented the synthesis and characterization of three new bromo substituted stilbene derivatives,p-3,4,5-trimethoxy-p'- 2,3,4,5,6-pentabromostilbene(C1),p-N,N-dimethylamino-p'-2,3,4,5,6-pentabromostilbene(C2) and p-N,N-diphenylamino-p'- 2,3,4,5,6-pentabromostilbene(C3) in this letter.The UV/vis absorption and photoluminescence were investigated in various solvents.The maximal absorption wavelength of C1 exhibited blue-shift to those of C2 and C3 in different solvents.No florescence emission could...     

Synthesis and properties of phenyl(methyl)-substituted 2- and 4-nitrosopyrimidines

Phenyl(methyl)-substituted 2- and 4-nitroso- and azoxypyrimidines were synthesized for the first time by the oxidation of phenyl(methyl)-substituted 2- and 4-hydroxy-aminopyrimidines by activated MnO₂, Ag₂CO₃ on zeolite, or BaMnO₄. Certain chemical properties of the synthesized nitrosopyrimidines were studied, such as reduction, nucleophilic substitution of the nitroso group, the condensation reaction with aniline and hydroxyaminopyrimidines.For Preliminary communication, see [1].DeceasedTranslated from Khimiya Geterotsiklicheskikh Soedinenii, No. 7, pp. 962–968, July, 1989.     

Aryl cations from aromatic halides. Photogeneration and reactivity of 4-hydroxy(methoxy)phenyl cation

The photochemistry of 4-chlorophenol (1) and 4-chloroanisole (2) has been examined in a range of solvents and found to lead mainly to reductive dehalogenation, through a homolytic path in cyclohexane and a heterolytic path in alcohols. Heterolysis of 1 and 2 in methanol and 2,2,2-trifluoroethanol offers a convenient access to triplet 4-hydroxy- and 4-methoxyphenyl cations. These add to pi nucleophiles, viz., 2,3-dimethyl-2-butene, cyclohexene, and benzene, giving the arylated products in medium to good yields. Wagner-Meerwein hydride and alkyl migration are evidence for the cationic mechanism of the addition to alkenes. Arylation (with no rearrangement) was obtained to some extent also in nonprotic polar solvents such as MeCN and ethyl acetate, reasonably via an exciplex and with efficiency proportional to the nucleophilicity of the trap (2,3-dimethyl-2-butene > cyclohexene > benzene).     

Arene diazonium saccharin intermediates: a greener and cost-effective alternative method for the preparation of aryl iodide

In the current protocol, the arene diazonium saccharin derivatives were initially produced from various substituted aromatic amines; subsequently, these intermediates were treated with a greener organic iodide for the preparation of the aryl iodide. We tried to choose low-cost, commercially available, biodegradable, recoverable, ecofriendly, and safe reagents and solvents. The arene diazonium saccharin intermediates could be stored in the liquid phase into a refrigerator for a long time with no significant loss activity. The outstanding merits of the current protocol (a) included the partial recovering of saccharin and tetraethylammonium salt, (b) reduce the use of solvents and the reaction steps due to eliminating separation and purification of intermediates, (c) good yield of the sterically hindered substrates, and (d) avoid the generation of heavy metal or corrosive waste.     

Azo coupling of 5-substituted furan-2(3H)-ones and 1H-pyrrol-2(3H)-ones with arene(hetarene)diazonium salts

5-Substituted furan-2(3H)-ones and 1-phenyl-1H-pyrrol-2(3H)-ones reacted with diazonium salts derived from substituted anilines and 1H-1,2,4-triazol-5-amine to give azo coupling products at the methylene group in the heteroring. The products were found to exist as hydrazone tautomers.     

A general method for the synthesis of 1-substituted (or unsubstituted)-4-carbomethoxy-2-imidazolin-5-ones

A general method for the synthesis of the title compounds by employing the reagent methyl $\text{N}$-(dicarbomethoxymethyl)methanimidate is described. The preparation, properties and reactions of the reagent are also reported.     

Synthesis of 1-substituted 5-alkyl(aryl)-1,3-dihydro-2<Emphasis Type="Italic">H</Emphasis>-pyrrol-2-ones. Azocoupling with diazonium salts

Reactions of 5-alkyl- and 5-aryl-3H-furan-2-ones with 1,3- and 1,4-binucleophiles of aromatic series were carried out for the first time under various conditions. In the presence of a base the reaction resulted in 1-R-1,3-dihydro-2Н-pyrrol-2-ones, under milder conditions intermediates were isolated, 4-aryl-4-oxobutanamides. The structure of the latter was proved by spectral methods. By an example of 1-R-1,3-dihydro-2Н-pyrrol-2-ones the possibility was demonstrated of their functionalization via introducing an aryldiazenyl fragment.     

Heck arylation of endocyclic enecarbamates with diazonium salts. Improvements and a concise enantioselective synthesis of (-)-codonopsinine

Total enantioselective synthesis of the natural (-)-codonopsinine was accomplished in seven steps with an overall yield of approximately 16% starting from the five-membered endocyclic enecarbamate 4. The total synthesis features a highly efficient and stereoselective Heck arylation of endocyclic enecarbamate 4 with p-methoxybenzenediazonium tetrafluoroborate and a stereoselective epoxidation/epoxide opening sequence as key steps.