The Mitsunobu Reaction: Origin,Mechanism, Improvements,and Applications

The Mitsunobu reaction is a widely used and versatile method for the dehydrative oxidation–reduction condensation of an acid/pronucleophile usually with a primary or secondary alcohol that requires the combination of a reducing phosphine reagent together with an oxidizing azo reagent. The utility of this reaction stems from the fact that it is generally highly stereoselective and occurs with inversion of the stereochemical configuration of the alcohol starting material. Furthermore, as carboxylic acids, phenols, imides, sulfonamides, and other compounds can be used as the acid/pronucleophile, this reaction is useful for the preparation of a wide variety of functional groups. This Focus Review of the Mitsunobu reaction summarizes its origins, the current understanding of its mechanism, and recent improvements and applications.     

Deoxypegan-1-one derivatives. synthesis and borohydride reduction of 3-[(E)-arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolin-1(2H)-ones

3-[(E)-Arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolin-1(2H)-ones were prepared by reaction of quinazolyl-2-propionic acid hydrochloride with aromatic aldehydes in acetic anhydride in the presence of Et₃N. 3-[(E)-Arylmethylidene]-1,2,3,9-tetrahydropyrrolo[2,1-b]quinazolin-1-ols were formed by reduction of the 3-arylidene derivatives with sodium borohydride in methanol, readily lost water when heated with acids, and were converted into 3-[(E)-arylmethylidene]-3,9-dihydropyrrolo[2,1-b]quinazolines. __________ Translated from Khimiya Prirodnykh Soedinenii, No. 5, pp. 463–467, September–October, 2006.     

Cathodic reduction of SO2 in the presence of organic dihalides

The reaction of the electrolytically generated SO ₂ ^– anion radical with 1,-dihalides is used for the synthesis of sulfur containing heterocycles like oxathiolane-, oxathiane-, thiane- and thiepane-oxides. 1,2-Dihalides are reductively deblocked to give olefines.

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Kathodische Reduktion von SO₂ in Gegenwart organischer Dihalogenide

Zusammenfassung Die Reaktion des elektrolytisch erzeugten SO ₂ ^– -Anionradikals mit 1,-Dihalogeniden führt zu schwefelhaltigen Heterocyclen wie Oxathiolan-, Oxathian-, Thian- und Thiepanoxiden. 1,2-Dihalogenide geben durch reduktive Eliminierung Olefine.

     

Electrocatalytic dehalogenation of α-bromoketones in the presence of Cp2TiCl2

Processes of direct and electrocatalytic (in the presence of electrochemically reduced Cp₂TiCl₂) reduction of three α-bromoketones containing the C(sp³)-Br or C(sp²)-Br bond, viz., 2-bromo-and 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-ones and α-bromo-acetophenone, were studied by cyclic voltammetry and preparative electrolysis. In all cases, the dissociative electron transfer proceeds via the concerted mechanism. Preparative electrolysis of these α-bromoketones in the presence of Cp₂TiCl₂ affords the reductive debromination products in 40–80% yield at low cathodic potentials (−0.85 V vs. Ag/AgCl/KCl). In the case of 2,6-dibromo-4,4-dimethylcyclohexa-2,5-dien-1-one in the potentiostatic regime, only one bromine atom can be eliminated selectively. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 5, pp. 977–983, May, 2007.     

Pheromone, 3.Mitt.: Eine einfache Methode zur Steuerung der Reduktion von α-Alkoxy-carbonylverbindungen

Summary Enantiomerically pure 1,2-diols bearing optionallysyn oranti configurated secondary hydroxylic groups are synthesized from acetal-protected cyanohydrins. After resolution of the diastereomers the cyanohydrins are converted into -alkoxy-ketones by Grignard-reaction followed by reduction using common chelating or non-chelating agents. Among others syntheses of enantiomerically pure pheromones,endo-Brevicomin,exo-Brevicomin and Dispalure are given as examples.

Prof. Dr. Hans Berbalk zum 70. Geburtstag gewidmet     

Effect of film thickness on the electro-reduction of molecular oxygen on electropolymerized cobalt tetra-aminophthalocyanine films

We studied the electrocatalytic activity of cobalt tetra-aminophthalocyanine (CoTAPc) for the reduction of molecular oxygen (O₂) on adsorbed monomeric and on electropolymerized films of different thicknesses on glassy carbon (GC) electrode. The polymeric films, denoted poly-CoTAPc, were first characterized by electrochemical impedance spectroscopy and it appears that the types of phenomena revealed to be occurring depend less on the film thickness in basic than in acid media. For O₂ reduction, the results showed that poly-CoTAPc is more active than the monomeric CoTAPc adsorbed on GC. Indeed, rotating ring-disk electrode data showed that polymeric CoTAPc promotes the four-electron reduction of O₂ to water in parallel to a two-electron reduction to give peroxide. On monomeric and thin films of poly-CoTAPc, a two-electron reduction mechanism predominates. In basic media the activity increases very slightly with thickness, whereas in acid media this increase is more pronounced. This parallels the observed behavior revealed by electrochemical impedance spectroscopy.     

(R)-2,3-Cyclohexylideneglyceraldehyde, a novel template for facile and simple entry into chiral hydroxy γ-lactones: synthesis of (−)-muricatacin

(R)-2,3-Cyclohexylideneglyceraldehyde 1 has been used in a simple and efficient synthesis of (−)-muricatacin 10. The required chiron, syn-alkanetriol 2a was prepared by the reduction of a ketone 3 derived from 1.     

Electrochemical Reduction of Monochlorinated Hydrocarbons at a Hydrophobic Zn/PTFE Composite‐Electroplated Zn Electrode in a Water‐Acetonitrile Mixture

Composite‐electroplating of zinc particles with polytetrafluoroethylene at a zinc substrate resulted in a working electrode which could be used at high negative potentials (to ?2.5 V vs. Ag/AgCl) without significant hydrogen evolution. The electrodes were characterized by SEM and CV and were used to detect organochloride compounds in a water‐acetonitrile mixture, by potential step methods.     

2-Trif luoromethyl-4H-thiochromen-4-one and 2-trif luoromethyl-4H-thiochromene-4-thione: Synthesis and reactivities

2-Trifluoromethyl-4H-thiochromene-4-thione obtained from 2-trifluoromethyl-4H-thiochromen-4-one and P₂S₅ reacts with aromatic amines, hydrazine hydrate, phenylhydrazine, and hydroxylamine at the C(4) atom of the chromene ring to give the corresponding anils, azine, hydrazones, and oxime of thiochromone. 2-Trifluoromethyl-4H-thiochromen-4-one is oxidized by hydrogen peroxide in AcOH into 4-oxo-2-trifluoromethyl-4H-thiochromene 1,1-dioxide and reduced by NaBH₄ to 2-trifluoromethyl-4H-thiochromen-4-ol or cis-2-(trifluoromethyl)thiochroman-4-ol. When treated with hydrazine hydrate, thiochromen-4-one gives 3(5)-(2-mercaptophenyl)-5(3)-trifluoromethylpyrazole. Published in Russian in Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 3, pp. 504–509, March, 2006.     

原子荧光光谱法测定砷过程中还原反应条件的优化

自然界中砷和砷的化合物一般可通过水、大气和食物等途径进入人体,危害人体健康,原子荧光光谱法测定砷含量被广泛应用。为准确测定样品中砷的含量,以原子荧光光谱法(AFS)测定土壤中总砷含量为例,重点研究高价态砷(Ⅴ)还原为低价态砷(Ⅲ)的实验条件,采用正交实验进行条件优化,建立适合的实验方法。通过设计L9(34)正交实验,高价态砷的还原反应与四个因素有关,即与反应温度、反应时间、盐酸加入量和硫脲的用量呈一定的正相关,结果表明,四个因素中硫脲用量的影响最为显著,其次是盐酸加入量、反应时间和反应温度。通过对四个因素的多水平检验,优化后的实验条件为：硫脲用量2.0 mL、盐酸加入量10%、反应时间20 min、温度20～35 ℃(即普通室温)。采用土壤标准物质验证优化后条件的可行性,得出砷的测定值在标准值范围内,RSD在2.2%～4.2%,精密度和准确性均满足质控要求。优化后的实验条件使得操作简便易行,提高了工作效率。