New olefinic functionalized disilanes. Synthesis and NMR spectroscopical investigations

The new olefinic substituted aminodisilanes, which are obtained from the reaction of organometallic reagents with aminochlorodisilanes, are converted into the chlorodisilanes by equilibration reactions or treatment with HCI. The resulting olefinic functionalized disilanes are identified by means of ²⁹Si, ¹³C, ¹H NMR and GC MS measurements.     

The stereodivergent aziridination of allylic carbamates, amides and sulfonamides

A stereodivergent protocol for the aziridination of a range of cyclic allylic amine derivatives has been developed. syn-Products can be obtained in >99:1 dr under H-bonded control and anti-products are obtained in >99:1 dr under steric control by judicious choice of the N-protecting groups.     

An efficient enantioselective synthesis of florfenicol via asymmetric aziridination

An efficient enantioselective synthesis of florfenicol is accomplished in 44.7% overall yield from commercially available p-(methylsulfonyl)benzaldehyde. Key features of this synthesis are the asymmetric aziridination reaction mediated by the Wulff’s catalyst in situ derived from (R)-VANOL and diastereoselectively ring-opening of (2S,3S)-fluoroaziridine 13.     

Synthesis of 4-cyanoethylated benzoxazines by visible-light-promoted radical oxycyanomethylation of olefinic amides with bromoacetonitrile

A facile and efficient protocol for the visible-light-promoted radical oxycyanomethylation of olefinic amides with bromoacetonitrile has been developed, affording a series of 4-cyanoethylated benzoxazine derivatives in moderate to excellent yields. The reaction featured with diverse functional group tolerance and mild reaction conditions.     

Selective debenzylation of benzyl esters by silica-supported sodium hydrogen sulphate

A new debenzylation of benzyl esters by silica-supported sodium hydrogen sulfate is described. The debenzylation could be achieved selectively and efficiently in good to excellent yields without affecting sensitive functional groups such as nitro, unsaturated bonds, and ethyl ester.     

Selective monoprotection of 1,4,7,10-tetraazacyclododecane via direct reaction with 4-nitrophenyl active esters

A simple, one-pot preparation of monoprotected 1,4,7,10-tetraazacyclododecanes via an efficient acylation reaction with 4-nitrophenyl active esters has been developed.     

Synthesis of densely functionalized cispentacin derivatives through selective aziridination and aziridine opening reactions: orthogonally protected di- and triaminocyclopentanecarboxylates

A novel substrate-directed synthetic route to a series of highly functionalized, orthogonally protected di- or triaminocyclopentanecarboxylate derivatives with multiple chiral centres from an unsaturated bicyclic β-lactam has been accomplished by applying stereoselective ring C–C double bond aziridination with chloramine-T and phenyltrimethylammonium tribromide, followed by regioselective aziridine opening with different N,O nucleophiles and hydrides. The functionalization strategy was successfully extended for access to enantiomerically pure orthogonally protected triaminocarboxylates.     

Selective deprotection and amidation of 2-pyridyl esters via N-methylation

The 2-pyridyl residue serves as a protecting group for various carboxylic acids. The protecting group is selectively cleaved under mild conditions via N-methylation of the pyridyl group. During the deprotection process, the various functional groups as well as the other ester moieties remain intact. The N-methylated active esters can be subsequently transformed into amides.     

Copper iodide-catalyzed aziridination of alkenes with sulfonamides and sulfamate esters

An efficient copper iodide-catalyzed aziridination of a variety of alkenes with sulfonamides and sulfamate esters as the nitrogen source and iodosylbenzene (PhIO) as the oxidant is reported herein. The reaction is operationally straightforward, applicable to a variety of alkenes containing electron-withdrawing, electron-donating, and sterically encumbered substrate combinations, and proceeds under mild conditions at room temperature in good to excellent yields.     

雪松烷二醇硼酸酯的合成及其不对称同系化反应

报道了手性试剂雪松烷二醇硼酸酯(3)的合成及其和二氯甲基锂进行不对称同系化反应,生成α-氯代硼酸酯4R和4S,其R/S的比率在25:1以上,并且有手性助剂容易回收的特点。通过对同系化产物4cR的单晶X衍射分析,发现其分子中的1,3-二氧杂-2-硼杂环戊烷为非平面结构,文中就这一结构特点进行了初步讨论,解释了雪松烷二醇硼酸酯容易水解的原因。     

Enzymatic synthesis of gallic acid esters

Esters of gallic acid were synthesized by enzymatic means using tannase fromAspergillus niger. Alcohols ranging from C₁ through C₁₂ and diols from C₃ through C₆ were tested and found to form esters in the presence of the enzyme.     

Palladium-catalysed arylation of acetoacetate esters to yield 2-arylacetic acid esters

The coupling reaction between ethyl acetoacetate and a number of aryl halides in the presence of palladium acetate, a bulky and electron rich phosphine and K₃PO₄ is described. The arylated acetoacetate ester is de-acylated under the reaction conditions resulting in the generation of 2-arylacetic acid esters, constituting a mild alternative to direct arylation of carboxylate esters.     

酸性酯交换-气相色谱-质谱法同时测定植物油中氯丙二醇酯和缩水甘油酯

建立了一种气相色谱-质谱同时测定植物油中3-氯丙二醇酯、2-氯丙二醇酯和缩水甘油酯的方法.称取0.25 g样品,依次加入内标工作液、四氢呋喃和酸性溴化钠溶液,50℃水浴反应15 min,加入6 g/L碳酸氢钠溶液终止反应,使用正己烷提取,上层液经氮气吹干后用四氢呋喃溶解.随后加入1.8％(v/v)硫酸-甲醇溶液于40℃...     

Site of protonation in the chemical ionization mass spectra of olefinic methyl esters

The H₂ and CH₄ chemical ionization mass spectra of the olefinic esters methyl acrylate, methyl methacrylate, methyl crotonate, methyl 3-butenoate, methyl 2-methyl-2-butenoate, methyl 3-methyl-2-butenoate and methyl cinnamate have been determined. In addition to the expected loss of CH₃OH from [MH]⁺, in many cases the protonated molecules also show loss of CO or CH₂CO with methoxy group migration to the positive ion centre, indicative of protonation at the double bond. These rearrangement reactions, which have analogies in electron impact mass spectra, result in chemical ionization mass spectra of isomeric molecules which show more substantial differences than the electron impact mass spectra. In the case of methyl cinnamate, isotopic labelling experiments show considerable interchange of the added proton with the ortho and meta phenyl hydrogens prior to CH₃OH or CH₂CO loss, although the extent of interchange is not the same for both cases.     

Selective demethylation of phosphorus esters

The selective cleavage of methyl phosphorus esters by t-butylamine is described.     

One-step synthesis of α-hydroxy-α-azinylcyanoacetic esters from α-nitro derivatives of α-azinylcyanoacetic esters

When boiled in aromatic hydrocarbons, solutions of α-nitro-α-azinylcyanoacetic esters of the pyrimidine, pyrazine, ands-triazine series gave the corresponding α-hydroxy derivatives of α-azinylcyanoacetic esters in high yields. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 7, pp. 1407–1409, July, 1997.     

Photo-Fries and Fries reaction of 5,8-dihydro-1-naphthyl esters

Systematic studies were performed on the photo-Fries and the Fries reaction of aliphatic, aliphatic unsaturated, aromatic and aromatic unsaturated esters of 5,8-dihydro-1-naphthol. The Fries reaction of 5,8-dihydro-1-naphthyl acetate in various solvents is also reported.     

Radical-mediated hydroxyalkylation of α,β-unsaturated esters

The radical-mediated hydroxyalkylation of α,β-unsaturated esters with alkyl iodides, trialkylborane, water and KF in THF gave the corresponding α-hydroxy esters. The synthetic advantage of the method was demonstrated by a short-step total synthesis of (±)-tanikolide.