Cross-coupling of alkenyl,aryl or allylic selenides and grignard reagents catalyzed by nickel-phosphine complexes

Alkenyl, aryl or allylic selenides smoothly couple with Grignard reagents in the presence of Ni(II)-phosphine complexes as catalysts to afford the corresponding unsaturated compounds in good yields. The reactivity order of coupling reaction with BuMgBr catalyzed by NiCl₂ [Ph₂PCH₂CH₂CH₂PPh₂] was found to be PhSeMe « PhCl > PhSMe by the competitive reactions.     

Triselenium dicyanide from malononitrile and selenium dioxide. One-pot synthesis of selenocyanates

Triselenium dicyanide is formed by the interaction of malononitrile and selenium dioxide in dimethylsulfoxide or dimethylformamide. Addition of aromatic amines, indoles and some active methylene compounds to this reaction mixture gives the corresponding selenocyanates in one-pot.     

A new general route to olefins from selenides

Olefins including alkylidenecyclopropanes are readily prepared from the corresponding selenides by reaction of base on the corresponding selenonium salt. The reaction also applies to cyclopropylsulfides.     

Unsymmetrical Diarylketones from Electron-rich Heterocyclic Arenes

Summary.  AlCl₃-mediated chlorocarbonylation of a first arene by oxalyl chloride followed by in situ Friedel-Crafts acylation of a second electron-rich arene expeditiously provides, in a one-pot procedure, either symmetrical or unsymmetrical benzophenones with yields ranging from 17–52%. Best results are obtained when the more activated substrate is used as the second arene. Another advantage is that the resultant benzophenone precipitates from the reaction mixture allowing facile workup. Corresponding author. E-mail: Poupaert@cmfa.ucl.ac.be Received October 4, 2002; accepted October 15, 2002 Published online March 6, 2003     

Reactivity of chlorodeoxypseudoephedrines with oxo-, thio-, and selenocyanates

Herein, the reactivity of chlorodeoxypseudoephedrine hydrochlorides with oxo-, thio-, and selenocyanate nucleophiles is reported. 1,3-Heterazolidine-2-iminium or ammonium salts were obtained stereoselectively in most cases. The hard–soft nature of the calcogen atom determines the mechanistic pathway via an S_N2 (X = O), aziridine intermediate (X = Se), or both (X = S). A simple method to synthesize stereoselectively the trans-isomer of 3,4-dimethyl-5-phenyl-oxazolidine-2-iminium chloride and the cis-isomer of 4-methyl-5-phenyl-oxazoline-2-ammonium chloride, was also found. In addition, heterazolidine-2-imines or amines were liberated from the corresponding salts [Cl⁻ or XCN⁻ (X = O, S, Se)] with aqueous NaOH. Finally, cis-3,4-dimethyl-5-phenyl-oxazolidine-2-iminium chloride, cis-4-methyl-5-phenyl-oxazoline-2-amine, and trans-4-methyl-5-phenyl-selenazoline-2-amine compounds were studied by X-ray diffraction.     

δ-lactones from grignard reactions : Their isolation and structure characterization

Grignard reactions on methyl 4-methyl, 5-oxo, 5-phenyl (pX substituted) pentanoates 1-6 (X = H, Me, F, Cl, Br, OMe) produced mixtures of cis-(7-11) and trans-(12-16) tetrahydro 5,6 dimethyl-6-phenyl -2H-pyran-2-ones. They were isolated by HPLC and characterized by ¹H and ¹³C techniques. The stereochemistry of Grignard reactions in THF with CH₃MgCl was determined at 0° and 60°.     

Stereospecific synthesis of divinyl diselenides from vinyl acetyl selenides

Vinyl halides react with MeSeLi in DMF to afford vinyl methyl selenides which are demethylated by the excess of the MeSeLi; the vinyl selenide anions thus obtained react with acetyl chloride to give vinyl acetyl selenides. This three steps one pot synthesis occurs with complete retention of configuration. The vinyl acetyl selenides are cleanly fragmented by electron transfer to the vinyl selenide anions; addition of iodine to the resulting solutions produced the divinyl diselenides with retention of configuration. The transformation of vinyl acetyl selenides into divinyl diselenides can also be induced by catalytic amounts of a solution of sodium in HMPA or of sodium methanethiolate.     

醋酸烯丙酯选择性地合成烯丙基硒醚

醋酸烯丙酯被Pd(PPh3)4-SmI2还原，并发生中间体π-烯丙基钯络合物的极性 反转，而后与芳基硒溴化物作用，生成烯丙基硒醚．     

Unsymmetrical and symmetrical diphosphazane ligands derived from o-phenylene phosphorochloridite

Two new diphosphazane ligands, PrⁱN(PPh₂)(PO₂C₆H₄) ( 1 ) and PrⁱN{P(O₂C₆H₄)}₂ ( 3 ), have been synthesized and characterized by spectroscopic data. The structure of 1 has been confirmed by single crystal X-ray diffraction. Crystal data: Monoclinic, C2/c, Z = 16, a = 34.149(5) Å, b = 9.717(6) Å, c = 29.439(5) Å, β = 125.11(2)°, V = 7991 ų, R = 0.058, R_w = 0.061. This compound shows two different P–N bond lengths (1.654 (4) and 1.743(4) Å) and a P–N–P angle of 120.7(2)°. Variable temperature ³¹P NMR measurements for 1 and 3 throw light on the nature of the conformers present in solution.     

Synthesis of chlorophyll‐a skeleton homologs using grignard reaction with methyl pyropheophorbide‐a

From methyl pyropheophorbide‐a (MPPa) (1), methyl 2‐formylmethyl‐2‐devinyl‐9‐ethylenedioxy‐9‐deoxopyropheophorbide‐a (2) and methyl 3‐acetyl‐9‐ethylenedioxy‐2‐devinyl‐9‐deoxopyropheophorbide‐a (3) were prepared. The Grignard reactions of 2 and 3 were performed using cycloalkyl magnesium bromides to afford cycloalkyl‐substituted sec‐alcohol 4 and tert‐alcohols 9a‐c, respectively. By the deprotection of the ethylenedioxy group, these alcohols were respectively converted to exocyclic ketones 5 and 10a‐c, which were dehydrated to give chlorins 6 and 11a‐c having an alkenyl function at the 2‐position. On the other hand, the oxidation and deprotection of the alcohol 4 gave a diketo chlorin 8.     

The reaction of o-nitro- and p-nitro-phenyl selenocyanates with arylthiols

The interaction of o-nitro- and p-nitro-phenyl selenocyanate with aromatic thiols p-thiocresol, p-chlorothiophenol, 4-bromothiophenol, o-mercaptobenzoic acid and pentafluorothiophenol in non-aqueous media and under an atmosphere of dry nitrogen has been investigated. The main products are the diselenide or the selenenyl sulphide depending on the reactants. Hydrogen cyanide is given in all cases. The IR and Raman spectra of the diselenides and selenenyl sulphides are considered.     

2－位甲（乙）酰基焦脱镁叶绿酸a甲酯的9－位羰基保护及其格氏反应

以焦脱镁叶绿酸α甲酯为起始原料，利用其2-位乙烯基的加成和氧化反应将乙 烯基转化成羟烷基，为了排除9-位羰基对后期化学反应的影响，首先通过乙二醇对 其进行保护，合成了9-羰基保护的焦脱镁叶绿酸的衍生物，再利用氧化反应将羟烷 基氧化成甲酰和乙酰基，进而成功地进行了格氏反应。所合成的焦脱镁叶绿酸α甲 酯的衍生物均经UV，IR，^1H NMR和元素分析确证。     

Synthesis of Symmetrical and Unsymmetrical Ureas Using Unsymmetrical Diaryl Carbonates

Appropriately substituted unsymmetrical diaryl carbonates react smoothly with primary amines to give the carbamates derived by nucleophilic displacement of the less electron rich aromatic substituent. Subsequent treatment of the carbamates with primary and secondary amines gives either symmetrical or unsymmetrical ureas in excellent yield and the overall process can be carried out as a “one pot” operation. Acetonitrile is the preferred solvent and addition of DBU facilitates the carbamate → urea transformation.     

A convenient,transition metal-free synthesis of difluoromethyl selenoethers from organic selenocyanates and TMSCF2H

An efficient and transition metal-free method for the synthesis of aryl or alkyl difluoromethyl selenides (RSeCF₂H) from the corresponding selenocyanates (RSeCN) and TMSCF₂H/t-BuOK is described. The reaction performed in THF at 0?°C for 24?h or at room temperature for 6?h supplied a series of RSeCF₂H in good to high yields. The successful preparation of difluoromethylselenolated sulfadimethoxine derivative and the scaled-up synthesis of 1-benzyl-5-((difluoromethyl)selanyl)indoline, as examples, suggested good practicability of this method. Advantages of the reaction include mild reaction conditions, good functional group tolerance, a wide range of substrates, and high efficiency. This protocol offered a number of novel difluoromethyl selenoethers, which would accelerate use of such compounds in the areas of life science.