91233-19-1Relevant articles and documents
4-Substituted 1-acyloxypyridine-2(1H)-thiones: Experimental and computational studies of the substituent effect on electronic absorption spectra
Jankowiak, Aleksandra,Kaszynski, Piotr
supporting information; experimental part, p. 7441 - 7448 (2010/01/16)
(Chemical Equation Presented) A series of eight 4-substituted 1-(adamantane-1-carbonyloxy)pyridine-2(1H)-thiones (1, X=H, OC7H 15, Me, CF3, SC3H7, CN, COOMe, and Cl) was prepared and characterized by UV-vis spectroscopy in MeCN and cyclohexane. The observed lowest energy transition, designated as πCS→ π*ring, exhibits a substantial substituent effect and λmax ranges from 333 (X=OC 7H15) to 415 nm (X=CN). Experimental λ max values for all esters except for 1b (X=OC7H 15) correlate with the σp - parameter (ρ = 0.41 ± 0.03, r2= 0.95). In contrast, the energy of the absorption band at about 295 nm, designated as πCS → π*CS, is practically substituent independent. Both absorption bands exhibit a modest negative solvatochromic effect. The experimental absorption energies correlate better with excitation energies calculated for N-acetyloxy analogues 2 with the ZINDO//DFT than with the TD-DFT//DFT method. Calculations for a series of 12 N-acetates 2 predict the most blueshifted π → π* transition for the alkoxy substituent and most red-shifted for the NO2 group relative to the parent 2a (X = H). 2009 American Chemical Society.
The invention of radical reactions. Part 39. The reaction of white phosphorus with carbon-centered radicals. An improved procedure for the synthesis of phosphonic acids and further mechanistic insights
Barton, Derek H. R.,Vonder Embse, Richard A.
, p. 12475 - 12496 (2007/10/03)
White phosphorus in tetrahydrofuran under argon reacts in a long radical chain reaction with carbon radicals derived from Barton PTOC esters. The reaction is initiated by traces of oxygen and strongly inhibited by TEMPO. From the duration of the induction period the chain length can be measured as approximately one million. Each P4 molecule can add up to two carbon radicals. Oxidation of the adducts provides a convenient synthesis of phosphonic acids in high yield. With H2O2 at 0°C oxidation to the appropriate phosphinic acids is fast. For sensitive natural products the further transformation to phosphonic acids is best carried out at room temperature with an excess of SO2. In this way even linoleic acid can be convened to the corresponding phosphonic acid in good yield without any attack on the skipped diene unit. TEMPO is also remarkable for its stabilization of white phosphorus in solution when exposed to oxygen. Likewise an ordinary phosphine, like tributyl phosphine, is also stabilized by small amounts of TEMPO.
The invention of radical reactions. Part XXXVII. A convenient radical synthesis of dialkyl diselenides from carboxylic acids
Barton, Derek H. R.,Fontana, Giovanni
, p. 11163 - 11176 (2007/10/03)
A new and convenient synthesis of dialkyl diselenides from carboxylic acids by Barton PTOC ester based radical chemistry is described. This method was especially successful when O-cholestan-3β-yl-2,2,2-trichloroselenoacetate and O-neopentyl selenobenzoate
N-hydroxypyridine-2(1H)-thione derivatives of carboxylic acids as activated esters. Part I. The synthesis of carboxamides
Barton, Derek H. R.,Ferreira, J. Albert
, p. 9347 - 9366 (2007/10/03)
The reaction between an acyl derivative of N-hydroxypyridine-2(1H)- thione (a Barton PTOC ester) and either an amine (primary or secondary), or the corresponding sulfenamide, led to the formation of a carboxamide in a clean transformation requiring minimal work-up and purification. The reaction with a sulfenamide is particularly useful since the only by-product, an unsymmetrical disulfide, is of both synthetic and biological value. In sterically demanding cases, Barton PTOC esters were more reactive towards benzenesulfenamides than to the corresponding free amines.
The Invention of Radical Reactions. XXXIII Homologation Reactions of Carboxylic Acids by Radical Chain Chemistry
Barton, Derek H. R.,Chern, Ching-Yuh,Jaszberenyi, Joseph Cs.
, p. 407 - 426 (2007/10/02)
Various carbon radicals can be generated from carboxylic acids via the corresponding Barton esters.These radicals can be used for the synthesis of longer chain homologues of the original acids.
A facile preparation method for α,α-difluoroalkanecarboxylic acids and esters. A formal difluoromethylene insertion to alkanecarboxylic acids using radical reaction
Okano, Takashi,Takakura, Nobuyuki,Nakano, Yuko,Okajima, Asako,Eguchi, Shoji
, p. 1903 - 1920 (2007/10/02)
Various alkyl radicals generated by the photoreaction of a series of Barton esters reacted with 1,1-dichloro-2,2-difluoroethene to give radical adducts as the major product accompanied with self-trapping products. Primary, secondary, tertiary, benzyl, and some unsaturated alkyl radicals as well as those with another functional group such as ether, carbonyl, and azide were applicable. Barton esters of diacids also afford 1:2 adducts with a small amount of 1:1 adducts and bis-self-trapping products except for the succinic case. These adducts were hydrolyzed with AgNO3/H2O-THF to α,α-difluoroalkanecarboxylic acids and methanolyzed with AgNO3/MeOH to the corresponding methyl esters. 4-Azido-2,2-difluorobutylic acid and the methyl ester were converted to difluoro-GABA and difluoro-γ-lactams.
The invention of radical reactions. Part XXV. A convenient method for the synthesis of the acyl derivatives of N-hydroxypyridine-2-thione
Barton,Samadi
, p. 7083 - 7090 (2007/10/02)
Treatment of the readily available di-N-oxide - of 2-thiopyridine disulfide 6 with tributylphosphine in the presence of a carboxylic acid provides a convenient and high yielding synthesis of the acyl derivatives 2 of N-hydroxy-2-thio-pyridone. Application of this procedure to the acids 17 and 18 gave, after irradiation in the presence of t-butylthill, the desired decarboxylated derivatives in high (>90%) yield.
Homologation of carboxylic acids by improved methods based on radical chain chemistry of acyl derivatives of N-hydroxy-2-thiopyridone
Barton, Derek H. R.,Chern, Ching-Yuh,Jaszberenyi, Joseph Cs.
, p. 5013 - 5016 (2007/10/02)
Reaction of substituted terminal olefins with carbon radicals generated carboxylic acids gives adducts that can be transformed to one carbon atom longer homo-acids in high overall yield. With 6b yields are very good and the conditions of hydrolysis exceptionally mild.
AN UNUSUAL REACTION BETWEEN THE ESTERS OF N-HYDROXY-2-THIOPYRIDONE AND ACTIVATED AZO COMPOUNDS
Barton, Derek H. R.,Ozbalik, Nubar,Vacher, Bernard
, p. 7385 - 7392 (2007/10/02)
The esters 1 of N-hydroxy-2-thiopyridone react smoothly at room temperature in a thermal reaction with diethyl azo-dicarboxylic ester to furnish adducts 2 of a novel structure.Photolysis of these adducts affords a convenient route to the little known tetrazanes 8.Azo compounds without electron withdrawing groups do not react.The Cookson reagent, however, is so reactive that it gives diacyl derivatives of type 14.
THE INVENTION OF RADICAL REACTIONS PART XVIII. A CONVENIENT SOLUTION TO THE 1-CARBON PROBLEM (R-CO2H --> R-13CO2H)
Barton, Derek H. R.,Ozbalik, Nubar,Vacher, Bernard
, p. 3501 - 3512 (2007/10/02)
Radicals generated by photolysis (W light) of esters derived from N-hydroxy-2-thiopyridone react with electrophilic isocyanides 2a and (in the presence of trifluoroacetic acid) 2b to give adducts of type 3.Convenient reaction procedures have been worked out to hydrolyse the adducts to amides of type 5, from which the original acid can be regenerated under mild conditions.The three important acids oleic, linoleic and arachidonic have all given smooth reactions.In suitable examples, quantitative evolution of carbon dioxide and incorporation of 13C without dilution have been demonstrated.This reaction sequence will be useful for the labelling in the carboxyl group of prostaglandins, leukotrienes, and the side chain carboxyls of peptides.
