2-Hydroxy-1,2,2-triphenylethanone as an efficient photolabile protecting group for carboxylic acids

The synthesis is reported of 2-hydroxy-1,2,2-triphenylethanone esters of carboxylic acids by the reaction between 2-chloro-1,2,2-triphenylethanone and a carboxylic acid in the presence of silver carbonate and silver tetrafluoroborate. Photolysis of the esters occurs rapidly on irradiation with a medium-pressure mercury lamp through quartz or Pyrex to return the carboxylic acid. The side product of the photolysis is benzo[b]phenanthro[9,10-d]furan, formed through a tandem process involving initial generation of 2,3-diphenylbenzofuran, photochemical cyclisation and re-aromatisation by aerial oxidation.     

Synthesis and reactions of novel substituted β-hydroxy-λ-imino esters

α-Iminoketones react with simple lithium ester enolates to give substituted β-hydroxy-λ-imino esters. Some reactions of these esters are reported.     

Synthesis of esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone

The esters of 4-hydroxy-5-phosphinyl-2-imidazolidinone were prepared by reaction of urea with the esters of 2-hydroxy-2-phosphinylethanal in acidic medium. The ir, ¹H nmr and ³¹P nmr spectral data of the products are reported. All the isolated products had cis configuration. The stereochemistry of their formation is discussed.     

Synthesis of γ-diketo carboxylic acids and their esters

Conclusions We have developed a method of obtaining -diketocarboxylic acids and their esters by acid hydrolysis of esters of-(5-methylfuryl)propionic acids.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 214–215, January, 1968.     

Synthesis of gross-conjugated polyenic dialdehydes and carboxylic acid esters

Conclusions Methylenemalonaldehyde was used in a convenient method for the synthesis of 4-aryl-and 4-heteroarylmethylenehepta-2,5-diene-1,7-dials and dimethyl esters of 6-aryl- and 6-heteroarylmethyleneundeca-2,4,7,9-tetraene-1,11-dioic acid.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 11, pp. 2614–2616, November, 1987.     

Synthesis of vinyl esters of organosilicon carboxylic acids

Conclusions The vinylation of -silicon-containing carboxylic acids by acetylene under the influence of zinc and cadmium salts was investigated. A method was found for producing organosilicon complex vinyl esters.     

On the photolysis of 1-Phenyl-2-hydroxy-2-methyl-propanone-1 in the presence of methylmethacrylate,styrene, and acrylonitrile: Laser flash photolysis studies

1-Phenyl-2-hydroxy-2-methyl-propanone-1 (I) has been irradiated in argonsaturated benzene solution containing various amounts of styrene (St), methyl-methacrylate (MMA) or acrylonitrile (AN) with 25 ns flashes of 347 nm light. The aim of this work was to elucidate the kinetics of (a) the reactions of monomers with the triplets of (I) and (b) the reaction of initiator fragment radicals with monomers. Upon applying the optical absorption detection method the rate constants (in l mol⁻¹ s⁻¹) of the reaction of triplets of I with the three monomers were determined as 7 × 10⁹ (St), 8 × 10⁶ (MMA) and 1 × 10⁷ (AN). Therefore, (I) is not appropriate for photocuring coating formulations on the basis of styrene. Radicals stemming from the α-scission of (I¹) react with the monomers with the following rate constants (in l mol⁻¹ s⁻¹): 4·7 ×10⁵ (St), 6·3 × 10⁵ (MMA) and 1·6 × 10⁶ (AN).     

Synthesis of novel 5-hydroxy-3-alkoxy- and 5-hydroxy-3-alkylthioindole-2-carboxamides

The preparation of several novel 5-hydroxyindole-2-carboxamides is described. A 5-benzyloxyindole ester was elaborated to the 3-bromo, 3-hydroxy, and 3-alkoxy ester intermediates followed by conversion to the amide and debenzylation. A related 5-acetyloxy indole ester was converted to 3-sulfinyl and 3-alkylthio intermediates before simultaneous amidation and removal of the 5-hydroxy protecting group.     

Synthesis of 2-hydroxy-3,5-diaryl-6-benzyl-γ-pyrones and their esters

Chemistry of Heterocyclic Compounds -     

Synthesis of some thioglycidyl esters of monobasic carboxylic acids

Thioglycidyl esters of monobasic carboxylic acids were synthesized by thioepoxidation of glycidyl esters of thiourea.Translated from Khimiya Geterotsiklicheskikh Soedinenii No. 5, pp. 588–590, May, 1989.     

Fragmentation of homoallylic alkoxides. Synthesis of propenyl and 2-methylpropenyl ketones from carboxylic esters

An efficient two-step synthesis of propenyl and 2-methylpropenyl ketones from carboxylic esters is described which uses as the key step the fragmentation of a potassium dihomoallylic alkoxide under mild thermolytic conditions.     

Synthesis of highly decorated chiral 2-nitro-cyclohexane carboxylic esters through microwave-assisted organocatalyzed cascade reactions

Starting from (E)-β-substituted-β-nitroacrylates and α,β-unsaturated ketones, a stereoselective organocatalyzed one-pot methodology allowed to synthesize highly decorated chiral 2-nitro-cyclohexane carboxylic esters. The reaction is promoted by Cinchona alkaloid-derived primary amines in the presence of an acidic co-catalyst and affords two diastereoisomers, in good yields and high enantiomeric excess (often higher than 90% ee). By replacing conventional heating with microwave irradiation, cleaner reactions in shortened times (from 48 h to 30 min) were obtained, with improved dr (80:20) and high ee (up to 94%). The application of microwave technology to this organocatalytic methodology allowed also employing C1 substituted enones, leading to cyclohexanones with four contiguous stereocenters in two isomers only, and up to 99% enantioselectivity.     

Photochemistry of carboxylic acids containing the phenyl and thioether groups: Steady-state and laser flash photolysis studies

The mechanisms for the direct photolysis of phenylthioacetic acid (PTAA) and S-benzylthioglycolic acid (SBTGA) in acetonitrile were investigated using steady-state and laser flash photolysis. For both compounds, a variety of stable photoproducts were found under steady-state, 254 nm irradiation of acetonitrile solutions. The products from the direct photolysis of PTAA included carbon dioxide (photodecarboxylation), acetic acid, diphenyl disulfide, diphenyl sulfide, thiophenol, thioanisole, di(phenylthio) methane, and S-phenyl benzenethiosulfate. The products from the direct photolysis of SBTGA included carbon dioxide, toluene, dibenzyl, dibenzyl sulfide, dibenzyl disulfide, thioglycolic acid, benzyl mercaptan, benzyl alcohol, and benzaldehyde. These stable photoproducts were identified and characterized using HPLC, GC, GC–MS, and UV–vis methods. Quantum yields were determined for the formation of the various stable products following steady-state irradiations in the absence and in the presence of oxygen. In laser flash photolysis (266 nm Nd:YAG laser) experiments, a variety of transients (e.g., phenylthiyl radical, benzyl radical, etc.) was found. For both substrates (PTAA and SBTGA), photoinduced CS bond cleavage was the main primary process. It was also found that for both acids, photoinduced CC bond cleavage occurred, but as a minor process relative to CS bond cleavage. Detailed mechanisms of the primary and secondary processes are proposed and discussed. The validity of these proposed mechanisms was supported by an analysis of the quantum yields of stable products and their transient precursors. Supplementary observations on reactions between the radicals (e.g., C₆H₅–S, C₆H₅–CH₂) and oxygen are also consistent with the proposed mechanisms.     

2-Halogenoethyl and 2-halogenoethylthiol esters of furan series carboxylic acids

The corresponding 2-chloroethyl (2-chloroethylthiol) esters are synthesized by the action of ethylene chlorohydrin (chloroethylmercaptan) on the acid chlorides of 5-nitrofuran carboxylic acid and 3-(5-nitrofuryl-2)acrylic acid. The acid chlorides of benzoic, furan carboxylic, and 3-(furyl-2)-acryllc acids react with ethylene sulfide, to give 2-chloroethyl esters of those acids. Ethylene oxide does not react with the acid chlorides of benzoic acid and furan series carboxylic acids either at room temperature or on heating at 50° for 1 hour.     

Synthesis and lactonization of 1-(2-hydroxy-1,1-dimethylethyl)-aziridine-2-carboxylic acid esters

The reaction of 2,3-dibromopropanoates with 2-amino-2-methyl-1-propanol in the presence of triethylamine gave a number of 1-(2-hydroxy-1,1-dimethylethyl)aziridine-2-carboxylic acid esters, which, under the influence of basic catalysts, were converted to a bicyclic lactone — 2,2-dimethyl-4-oxa-1-azabicyclo[4.1.0]heptan-5-one. The effect of the structure of the substrate and the nature of the lactonizing agent on the rate of cyclization was studied. Two new catalysts for the cyclization of hydroxy esters to lactones, viz., CsF/Al₂O₃ and Cs₂CO₃/18-crown-6, are proposed.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1340–1343, October, 1988.     

On the Z-E photoisomerization of chiral 2-pentenoate esters: stationary irradiations, laser-flash photolysis studies, and theoretical calculations

Chiral pentenoates 1-3 in both Z and E isomeric forms underwent stationary irradiations in several solvents and in the presence of different photosensitizers. The photostationary-state ratio has been determined for each Z/E couple showing a predominance of the thermodynamically more stable isomer for 1 and 3. Moreover, transient species were generated by pulsed laser excitation and detected by their characteristic ultraviolet absorptions, being the first time that enoate-originated triplets are detected. Stern-Volmer quenching studies afforded a quantitative measure for the efficiency of the photosensitization processes induced by benzophenone or acetophenone and allowed the determination of the corresponding quenching rate constants. Density functional calculations permitted the determination of the geometries and the energies of the diastereomeric excited states. Two diastereomeric orthogonal and two diastereomeric planar structures result as a consequence of the presence of a chiral substituent. The orthogonal triplets are the energy minima in all cases, whereas the planar triplets are the transition states linking these orthogonal structures, the corresponding energy barriers being 8-10 kcal mol(-1) for enoates 1-3. The computed S(0) to T(1) excitation energies show a trend which is consistent with the quenching rate constants. On the other hand, the triplet lifetimes determined for 1 and 2 are unusually long (1-20 micros) if compared with the data already described for several enones, in the range of nanoseconds. This fact has been rationalized from calculations of spin-orbit coupling at several points of the T(1) potential energy surface. This coupling is maximum for structures with a torsional angle close to 45 degrees, which are 4-5 kcal mol(-1) above the minima of T(1). Calculations done on the hypothetical aldehyde 4 and methyl vinyl ketone show much lower energy barriers, thus accounting for the shorter lifetimes reported for enone triplets.     

A novel one-step synthesis of 2-substituted 6-azaindoles from 3-amino-4-picoline and carboxylic esters

Dilithiation of 3-amino-4-picoline (1) was achieved with sec-BuLi at room temperature. Condensation of the resulting dianion (2) with carboxylic esters afforded a wide range of 2-substituted 6-azaindoles in good yields.     

Synthesis of carboxylic esters using formaldehyde dimethyl dithioacetal S,S-dioxide

Formaldehyde dimethyl dithioaoetal S,S-dioxide ($\text{1}$) reacted uith an alkyl bromide or a 2-alkenyl bromide ($\text{8}$) under phase-transfer sonditions using 50% aq. NaOH to give an alkyl or 2-alkenyl derivative of $\text{1}$, whereas, in the reaction with $\text{8}$ in the presence of Kg₂CO₃KI in HMPA, $\text{1}$ formed a 1-alken-3-yl derivative. Transformation of these products into the corresponding carboxylio esters uae also described.     

p-Nitrobenzenesulfenate esters as precursors for laser flash photolysis studies of alkyl radicals

A series of p-nitrobenzenesulfenate esters was used in laser flash photolysis (LFP) studies to generate alkoxyl radicals that fragmented to give the (2,2-diphenylcyclopropyl)methyl radical. Rate constants for the beta-scission reactions increased as a function of the carbonyl compound produced in the fragmentation reaction in the order CH2O < MeCHO < Me2CO < PhCHO < Ph2CO and increased with increasing solvent polarity. For alkoxyl radicals that fragment to produce benzaldehyde and benzophenone, the beta-scission reactions are faster than 1,5-hydrogen atom abstractions when the incipient carbon radical is as stable as a secondary alkyl radical, and this entry to carbon radicals can be used in LFP kinetic studies.     

Synthesis and antifungal activity of carvacrol and thymol esters with heteroaromatic carboxylic acids

Aiming to obtain the more effective pathogen inhibitive ingredients and explore the influence of introducing different heterocyclic units to carvacrol and thymol esters, twenty ester derivatives with different heterocyclic units were synthesized. And the in vitro antifungal activity of title compounds against five plant pathogenic fungi was evaluated by mycelium growth rate method. The results showed that some carvacrol and thymol esters showed good to excellent antifungal activity, and compound 9d (4-bromo-5-isopropyl-2-methylphenyl picolinate) exhibited a broad antifungal spectrum. Preliminary study indicated that the introduction of furan, thiophene and pyridine unit could enhance the antifungal activity of carvacrol and thymol esters against Botrytis cinerea and a bromine atom on the para position of benzene moiety could enhance their antifungal activity.