Reaction of Polymer-supported Selenovinyl Bromide with Grignard Reagents： A Facile Route to the Synthesis of （E）-1, 2-Disubstituted Olefins

Polymer-supported selenovinyl bromide, easily prepared from polymer-supported selenenyl bromide with acetylene, reacts with different Grignard reagents using a step-by-step strategy to obtain （E）-1, 2-disubstituted ethenes in good yields.     

SNAr reactions of β-substituted porphyrins and the synthesis of meso substituted tetrabenzoporphyrins

Reaction of 2,3,7,8,12,13,17,18-octaethylporphyrin with LiR reagents containing functional groups readily yields meso substituted derivatives suitable for further transformations with residues such as -p-C₆H₅Br, -p-C₆H₅-CCH, -p-C₆H₅-NH₂ or -(CH₂)₃-CHCH₂. Similar reactions of tetrabenzoporphyrin with alkyllithium reagents afforded the first entry into meso mono- and dialkylsubstituted tetrabenzoporphyrins while reaction of bicyclo[2.2.2]oct-type masked isoindole precursors with LiR followed by in situ retro-Diels-Alder reaction also afforded the 5-phenyl and 5,10-diphenyltetrabenzoporphyrins in high purity.     

Highly substituted 2,3,7,8,12,13,17,18-octaethylporphyrins with meso aryl residues

Highly substituted porphyrin-bearing meso aryl groups are useful compounds for optical applications and for studies on the interrelationship between the substituent pattern, macrocycle conformation and physical properties. They serve as biomimetic models for the function of tetrapyrroles in nature and help to elucidate modulation of cofactor properties through conformational effects. Using a sequence of lithium organic substitution reactions the synthesis of novel free base 5,10-A₂- and 5,10-AB-2,3,7,8,12,13,17,18-octaethylporphyrins bearing donating groups such as -OMe and -NMe₂ on the aryl-substituent was achieved. Larger aromatic residues (1-naphthyl, 9-anthracenyl and 9-phenanthrenyl) could be introduced into the macrocycle system as well, and these systems were used for the preparation of highly substituted porphyrins with a mixed substituent pattern. Using phenanthrenyl derivatives, the complete series of meso phenanthrenyl substituted octaethylporphyrins was successfully synthesized and the palladium complexes were prepared for photophysical investigations. Structural studies clearly showed the influence of individual substituents on the conformation of the tetrapyrrole macrocycle and conformational analyses revealed the variation of the underlying distortion modes depending on the type and arrangement of the meso substituents.     

Reaction and sensing of octafluorocyclopentene with 1,5-diazabicyclo[4,3,0]non-5-ene

Reactions of octafluorocyclopentene (C₅F₈) with 1,5-diazabicyclo[4,3,0]non-5-ene (DBN) are studied by analyses of an isolated product and optical spectra from the viewpoint of applications to gas-sensors. Obtained results suggest that nucleophilic reactions of DBN proceed toward the double bond of C₅F₈ molecule accompanied with hydroxide anion attack on carbon-fluoride bonds of C₅F₈ moiety under ambients, forming unique C₅F₈-modified adducts. The present reaction is conducive to a new type of technologies for quick and selective sensing that can be used to develop alarm systems in the field of the environment and etching processing factories.     

Reactions of novel trifluoromethyl propargylic carbocation with carbon nucleophiles

Trifluoromethyl propargylic carbocation [I] generated from the reaction of 1-amino substituted 3-trifluoromethyl-2-propynyl trimethylsilyl ether 1 with TMSOTf in CH₂Cl₂ at −15 °C, followed by warming to room temperature reacted with 1.2 equiv of substituted benzenes, RMgBr and allylsilane to give the enones 3a-l and 5, respectively. The reaction of [I] with anisole, followed by treatment with Grignard reagents afforded the corresponding allyl amine derivatives 7, which underwent cyclization reaction to give indene derivatives 8 by using 2 equiv of TMSOTf.     

Direct substitution of propargylic alcohol with oxygen, nitrogen, and carbon nucleophiles catalyzed by molybdenum(VI)

Efficient and direct substitution of propargylic alcohol with a variety of oxygen, nitrogen, and carbon nucleophiles catalyzed by MoO₂(acac)₂/NH₄PF₆ system was developed. The functional alkynes were obtained in modest to good yields with this versatile and practical protocol.     

New reactivity of hydroxyallylpyridyl derivatives as C-3 carbon nucleophiles

Hydroxyallylpyridyl derivatives exhibited a peculiar thermal behavior likely ascribed to the weak acidity of the ‘picoline-type’ hydrogen atom on the C-1 carbon of the allyl residue, leading to allyl inversion products. The unprotected alcohol reacted as ‘vinylogous picoline’ carbon nucleophile with strongly activated heterocyclic counterparts. A mechanistic rationale for this unprecedented reactivity was proposed.     

Nucleophilic substitution of 4-bromomethyltriazolium with different nucleophiles

1,2,3-Triazolium salts draw much attentions in recent years. We developed a new synthetic method to heteroatom-functionalized triazoliums via nucleophilic substitution of 4-bromomethyltriazolium. This method afforded triazoliums with different S, N, and O heteroatom-substituents. Moreover, S_N2′ reaction was observed with alcohols or hydroxides. In addition, debromination and debromomethylation reaction occurred in some cases.     

Regioselectivity in the reactions of polyfunctionalised pyrroles with nucleophiles

The polyfunctionalised pyrrole, 3,5-dichloro-1H-pyrrole-2,4-dicarbaldehyde reacts with secondary amines by condensation with the 2-carbaldehyde to give methylene-substituted pyrroles, while its N-alkyl derivatives undergo substitution of the 5-chloro group to give 5-substituted pyrroles.     

Reactions of 3-R-5-nitropyridines with nucleophiles: Nucleophilic substitution vs conjugate addition

A number of 3-R-5-nitropyridines were synthesized and their reactions with various types of nucleophiles were investigated. The reaction outcome depends on the nature of a nucleophile: in case of anionic O-, N- and S-nucleophiles the previously unreported substitution of non-activated nitro group occurred while carbon nucleophiles underwent dearomatization of the pyridine ring with the formation of products of 1,2- and 1,4-addition.     

Reactions of methylchlorodisilanes with Grignard reagents

Reactions of Cl₂MeSiSiMeCl₂ with RMgCl make it possible to obtain and isolate pure disilanes containing a smaller number of functional groups, namely, RMeClSiSiMeCl₂ (R = Ph), RMeClSiSiMeRCl (R = Prⁱ, Ph), and R₂MeSiSiMeRCl (R = Buⁱ). The reaction of Cl₂MeSiSiMeCl₂ with BuⁿMgCl is the least selective. The chlorides obtained were reduced with LiAlH₄ into the corresponding hydrides.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 954–957, May, 1995.     

Efficient synthesis of unsymmetrical diaryl thioethers via TBAF-mediated denitrative substitution of nitroarenes with PhSTMS under mild and neutral conditions

Tetrabutylammonium fluoride(TBAF) effectively facilitated a denitrative substitution reaction of electron-deficient nitroarenes with phenylthiotrimethylsilane(PhSTMS) under mild and base-free neutral conditions at room temperature,providing a practical and efficient synthesis of useful unsymmetrical diaryl thioethers.Nitroarenes bearing ortho-and para-positioned electron-withdrawing groups are the most reactive substrates,indicating that this reaction most possibly proceeded via the nucleophilic aromatic substitution(S_NAr) mechanism.     

The first nucleophilic aromatic substitution of suitably activated 2-methoxyfurans with Grignard reagents

The reaction of 2-methoxyfuroates 1 with Grignard reagents 2 leads to tertiary alcohols or S_NAr products depending on the position of the alkoxycarbonyl group. OMe-Displacement occurs only for 3-substituted derivatives. It takes place even for 3-acetyl-2-methoxyfuran while the presence of a further ester function at 4 position induces the formation of the sole 4-tertiary alcohol. The OMe-substitution has been verified for a wide range of furans and Grignard reagents and low yields have been found only in the reactions with the benzylic and allylic reagents which are delocalized anions. A mechanistic interpretation is given.     

A highly regio- and chemoselective addition of carbon nucleophiles to pyrimidinones. A new route to C4 elaborated Biginelli compounds

Ethyl 6-methyl-pyrimidine-2-one-5-carboxylates react with C-nucleophiles in a diversity oriented synthetic sequence to afford C4 substituted congeners of medicinally potent Biginelli dihydropyrimidinones, in a highly regioselective manner.     

Synthesis of substituted uracils by the reactions of halouracils with selenium, sulfur, oxygen and nitrogen nucleophiles under focused microwave irradiation

Under microwave irradiation, the nucleophilic substitution reactions of halouracils with selenium, sulfur, oxygen and nitrogen nucleophiles was complete within several minutes with yields up to 99%. The method using microwave irradiation is superior to those conducted under conventional heating processes.     

Reaction pathways of zirconocene-catalyzed silylation of alkenes with chlorosilanes

Reaction pathways as well as stereochemistries and stoichiometries of zirconocene-catalyzed silylation of olefins with chlorosilanes in the presence of ⁿBuMgCl were studied and discussed in detail. Rate determining steps were examined by kinetic studies and labeling experiments.     

Nucleophilic aromatic substitutions on 4,5-dicyanopyridazine. Pyrrole and indole systems as carbon nucleophiles

4,5-Dicyanopyridazine was found to react with pyrrole and indole counterparts not only as heterocyclic azadiene in inverse electron-demand Hetero Diels–Alder reactions, as previously evidenced, but even as a very reactive heterocyclic electrophile at C-4 carbon, in formal S_NAr2 processes where a CN group acts as leaving group. In particular, operating in acetic acid as solvent, nucleophilic addition–elimination sequences allowed a facile access to pyrrolyl- and indolylpyridazines, through the corresponding 1,4-dihydropyridazine adducts.     

A study of the reaction of n-BuLi with Ti(Oi-Pr)4 as a method to generate titanacyclopropane and titanacyclopropene species

The use of the combination of reagents Ti(Oi-Pr)₄/n-BuLi, introduced by the group of J.J. Eisch in 2001, has only found a few applications so far, with sometimes conflicting observations. This article describes a study aimed at clarifying the nature, the stability and the reactivity of the active organometallic species involved. Reactions with CO₂ and other trapping reagents reveal that it is generated within a few minutes at 0 °C in THF, where it can be considered to be stable for 30 min. Most of our results are consistent with the expected titanacyclopropane nature of this reagent but some observations suggest that the chemistry at play may be more complicated.