Photoredox-catalyzed deoxyfluorination of activated alcohols with Selectfluor®

Herein we disclose a deoxyfluorination of alcohols with an electrophilic fluorine source via visible-light photoredox catalysis. This radical-mediated C–F coupling is capable of fluorinating secondary and tertiary alcohols efficiently, complementing previously reported nucleophilic deoxyfluorination protocols.     

Ternary complexes of substituted catechols and catecholamines

Stability constants of the ternary complexes [CuAL] whereA = 5-Nitro-1,10-phenanthroline, bis(2-pyridyl) ketone (DPK) orbis(2-pyridyl)amine (DPA) andL is the dianion of catechol, tiron, protocatechic acid, pyrogallol, 1,8-dihydroxynaphthalene, catecholaldehyde, 2,3-dihydroxynaphthalene, dopamine or adrenaline have been determined by potentiometric titration in dioxane water (1:1 v/v) medium using a SCOGS computer programme. The observed trend of stability is explained on the basis of the nature of substitution over the ligands, chelate ring size and also the composition of mixed solvent in case of DPK. Structural changes in DPK have also been discussed as a function of pH, composition of medium and coordinating mode of the secondary ligand in the ternary complexes.     

Recognition of chiral catechols using oxo-titanium phthalocyanine

Oxo-titanium phthalocyanine (TiOPc) derivatives of catechin and hematoxylin (natural ortho-diol type chiral compounds) have been prepared and characterized by spectral and chromatographic techniques. It is demonstrated that the TiOPc unit is an excellent template for chiral recognition through its isolated Q-transitions. The formation of a helical dimeric complex with hematoxylin induces strong CD-activity in the Q-band region. Ab initio geometry optimizations were combined with a Kuhn-Kirkwood coupled-oscillator mechanism to obtain the absolute configuration of hematoxylin. In addition, it is shown that the described chiroptical recognition method is sensitive to slight conformational changes.     

Copper-assisted oxidation of catechols into quinone derivatives

Catechols are ubiquitous substances often acting as antioxidants, thus of importance in a variety of biological processes. The Fenton and Haber–Weiss processes are thought to transform these molecules into aggressive reactive oxygen species (ROS), a source of oxidative stress and possibly inducing degenerative diseases. Here, using model conditions (ultrahigh vacuum and single crystals), we unveil another process capable of converting catechols into ROSs, namely an intramolecular redox reaction catalysed by a Cu surface. We focus on a tri-catechol, the hexahydroxytriphenylene molecule, and show that this antioxidant is thereby transformed into a semiquinone, as an intermediate product, and then into an even stronger oxidant, a quinone, as final product. We argue that the transformations occur via two intramolecular redox reactions: since the Cu surface cannot oxidise the molecules, the starting catechol and the semiquinone forms each are, at the same time, self-oxidised and self-reduced. Thanks to these reactions, the quinone and semiquinone are able to interact with the substrate by readily accepting electrons donated by the substrate. Our combined experimental surface science and ab initio analysis highlights the key role played by metal nanoparticles in the development of degenerative diseases.

An antioxidant catechol transforms following intramolecular redox reactions into highly reactive oxygen species, a semiquinone and a quinone, on copper.     

Reactive diene for synthesis of substituted catechols

(2R,3R)-2,3-Dimethoxy-2,3-dimethyl-5,6-dimethylene-1,4-dioxane has been synthesized and is a highly efficient diene in Diels-Alder reactions. Reaction with acetylenic dienophiles provides a simple route to substituted catechols. Reactions with some ethylenic dienophiles are also reported.     

Solid-Phase Nucleophilic Fluorination

This study demonstrates solid-phase nucleophilic fluorination. Polymer-bound 1-phenoxy-2-sulfonyloxyethane, as a model compound, is converted to a fluorinated compound in a short time. Furthermore, this method is applied to synthesize a precursor of 2-deoxy-2-fluoro-D-glucose by solid-phase synthesis using a microwave oven.     

Nucleophilic proteolytic antibodies

Proteolytic antibodies appear to utilizecatalytic mechanisms akin to nonantibody serine proteases, assessed from mutagenesis and protease-inhibitor studies. The catalytic efficiency derives substantially from the ability to recognize the ground state with high affinity. Because the proteolytic activity is germline-encoded, catalysts with specificity for virtually any target polypeptide could potentially be developed by applying appropriate immunogens and selection strategies. Analysis of transition-state stabilizing interactions suggests that chemical reactivity ofactive-site serine residues is an important contributor to catalysis. A prototype antigen analog capable of reacting covalently with nucleophilic serine residues permitted enrichment of the catalysts from a phage-displayed lupus light-chain library. Further mechanistic developments in understanding proteolytic antibodies may lead to the isolation of catalysts suitable for passive immunotherapy of major diseases, and elicitation of catalytic immunity as a component of prophylactic vaccination.     

Nucleophilic trifluoromethylation of arylidenemalononitriles

A method for the nucleophilic trifluoromethylation of arylidenemalononitriles using Me₃SiCF₃ is described. The reaction is carried out in dimethylformamide in the presence of AcONa as a Lewis base, and affords products of Michael addition in high yield.     

One-pot synthesis of tertiary alkyl fluorides from methyl oxalates by radical deoxyfluorination under photoredox catalysis

Tertiary alkyl fluorides have been prepared from methyl oxalates derived from tertiary alcohols by a sequential one-pot hydrolysis/photoredox catalyzed radical deoxyfluorination sequence. The reaction operates under mild conditions and tolerates a wide range of functional groups. This method provides an alternative approach to ionic deoxyfluorination transformations for the incorporation of Carbone–Fluorine quaternary centers into organic molecules.     

Nucleophilic reactions of polydialkylcyclosilazanes

A study is made of the catalytic condensation polymerization of polydialkylcyclosilazanes [RR'SiNH]_n (n=3,4; R=CH₃, C₂H₅; R'=C₂H₅, C₄H₉, C₆H₁₃, C₉H₁₉) in the presence of small amounts of nucleophilic reagents, to give compounds of the general type R₅R₆'Si₆N₃(NH)₂ and oligomers. The reactivities of polydialkylsilazanes decrease with increase in aliphatic group chain length.     

Nucleophilic reactions of polydialkylcyclosilazanes

A study is made of the catalytic condensation polymerization of polydialkylcyclosilazanes [RR'SiNH]_n (n=3,4; R=CH₃, C₂H₅; R'=C₂H₅, C₄H₉, C₆H₁₃, C₉H₁₉) in the presence of small amounts of nucleophilic reagents, to give compounds of the general type R₅R₆'Si₆N₃(NH)₂ and oligomers. The reactivities of polydialkylsilazanes decrease with increase in aliphatic group chain length.     

Nucleophilic isomerization of perfluoropentenes

Conclusions The isomerization of perfluoro-1-pentene by CsF in polar aprotic solvents leads to a mixture of trans- and cis-perfluoro-2-pentene in an isomer ratio of 61.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2646–2647, November, 1981.     

Nucleophilic cationization reagents

Nucleophilic cationization reagents fitted with aminooxy groups are described. Practical syntheses of mono- and bis-aminooxy tetraalkylammonium iodides including N-hydroxyethyl-functionalized analogs are reported. An oximation example using one of the reagents is presented to illustrate their use in synthesis of cationic materials.     

Nucleophilic thiylation of carvone

The reaction of carvone with 2-mercaptoethanol and an S-phenoxybenzylisothiuronium salt in the presence of sodium ethoxide was found to proceed exclusively at the endocyclic double bond. Under these same conditions, an S-allylisothiuronium salt reacted to produce a bis-sulfide with the menthene structure. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 1, pp. 44–46, January–February, 2007.