N-Substituted C-diethoxyphosphorylated nitrones as useful synthons for the synthesis of α-aminophosphonates

A convenient method for the synthesis of N-substituted C-phosphorylated nitrones 2 from hydroxymethylphosphonates via successive Swern oxidation and treatment with respective hydroxylamines is reported for the first time. Moderate (20%) to excellent (up to 90%) diastereoselectivities in cycloadditions of nitrone 2a and terminal alkenes were observed with trans C5-substituted isoxazolidines predominating. In ZnCl₂-catalysed cycloadditions, mixtures enriched in cis diastereoisomers were produced.     

Direct Michael addition to electron-deficient alkenes using diorganyl dichalcogenides (Te/S) and NaBH4/PEG-400

Nucleophilic species of tellurium and sulfur were generated in situ from the reaction of the respective diorganyl dichalcogenides with NaBH₄ in PEG-400 as solvent and selectively added to electron-deficient alkenes. Chalcogenolate anions were directly added at mild conditions by this simple procedure and in all cases furnished the respective Michael adducts in short reaction times and good yields.     

Selective copper(II)-catalyzed aerobic oxidative cleavage of aromatic gem-disubstituted alkenes to carbonyl compounds under neutral and mild conditions

Three copper(II) catalytic systems, CuCl₂·2H₂O, CuCl₂·2H₂O+phenanthroline, and [Cu(μ-Cl)Cl(phen)]₂ were used to cleave alkenes to their corresponding carbonyl compounds under aerobic and neutral conditions. [Cu(μ-Cl)Cl(phen)]₂ shows enhanced selectivity over the other two catalytic systems. The oxidative cleavage reactions were carried out in mixed H₂O/THF solvent system under oxygen (4 atm) at 60°C. The real oxidant is 2-hydroperoxytetrahydrofuran, which is generated in situ in the process through the reaction between THF and oxygen catalyzed by copper(II). The cleavage reactions are selective for aromatic gem-disubstituted alkenes. Aromatic internal alkenes are slow to be oxidized, and both aliphatic terminal and internal alkenes are inert to oxidative cleavage. Free radical scavenger 2,2,6,6, tetramethylpiperidinyl-1-oxyl (TEMPO) deactivates the reaction indicating the involvement of free radical path in the reaction mechanism.     

Synthesis of fluorinated N-aminoaziridines: access to new CF3-peptidomimetics

A series of fluorinated N-aminoaziridines have been synthesized by the PhI(OAc)₂-mediated aziridination procedure. The reaction was carried out with various protected hydrazides and fluorinated alkenes. The reaction was extended to alkenes bearing an amino acid and the ring opening of the CF₃–N-aminoaziridines has been investigated.     

The application of pyranoside phosphite-pyridine ligands to enantioselective Ir-catalyzed hydrogenations of highly unfunctionalized olefins

Eight (biaryl)phosphite/pyridine ligands 1–2a–d have been prepared by the modular functionalization of positions C-2 and C-3 of two d-glucopyranoside backbones. The chiral ligands were examined in the iridium-catalyzed asymmetric hydrogenation of poorly functionalized alkenes, as a function of the relative position of the coordinating groups and the geometric properties of the biaryl phosphite moieties. Enantiomeric excesses of up to 90% were achieved in the hydrogenation of E-2-(4-methoxyphenyl)-2-butene by using 1a and 1c, which seemingly combine the beneficial effect of the phosphite at the 2-position with the matching (R_ax)-configuration of their encumbered biaryl substituents. The results of the hydrogenation of more challenging substrates, such as Z-trisubstituted alkenes, alkenes with a neighboring polar group or demanding 1,1-di-substituted alkenes, generally confirmed this trend, and in some significant cases, the chiral hydrogenated products were isolated with ees of 65–79%.     

Cobalt complex in a room temperature ionic liquid: A convenient recyclable reagent for catalytic epoxidation of cyclic alkenes

Co-catalyzed epoxidation of cyclic alkenes proceeds in ionic liquid media (1-ethyl-3-methylimidazolium hexafluorophosphate). Epoxidation of the alkenes to respective epoxides was greatly accelerated by the use of a cobalt-based catalyst in the presence of H₂O₂ as an oxidant. The catalyst in ionic liquid [Emim]PF₆ was recycled and reused for about seven times.     

Selenium-catalyzed iodohydrin formation from alkenes

A new simple method for catalyzed iodohydroxylation of alkenes using stoichiometric amounts of water is described. The iodohydrins were prepared in good yields from the corresponding alkenes using N-iodosuccinimide, 2 equiv of H₂O, and catalytic amounts of diphenyl diselenide in MeCN.     

Reaction of CBrF2-CBrF2 with hydrazones of aromatic aldehydes: Novel efficient synthesis of fluorocontaining alkanes, alkenes and alkynes

An olefination of hydrazones of aromatic aldehydes by CBrF₂-CBrF₂ under copper catalysis was investigated. In situ prepared aldehydes hydrazones were converted to (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by reaction with CBrF₂-CBrF₂ in the presence of CuCl. Subsequent elimination of HF by sodium hydroxide resulted in stereospecific formation of fluorocontaining alkenes. Elimination proceeds stereoselectively, only Z-isomers of alkenes are formed. Elimination of two molecules of HF from (3-bromo-2,2,3,3-tetrafluoropropyl)arenes by treatment with potassium tert-butoxide leads to formation of (bromodifluoromethyl)alkynes. As a result a simple and efficient transformation of aromatic aldehydes to range of various fluorinated alkanes, alkenes and alkynes was elaborated.     

气相色谱-质谱表征甲醇制烯烃副产汽油中的C5～C7烯烃

采用气相色谱-质谱(GC-MS)对甲醇制烯烃(MTO)副产汽油中的C5~C7烯烃进行了详细的定性表征,对MTO副产汽油中的49个单烯烃、11个二烯烃和9个环烯烃共计69个C5~C7烯烃组分在聚甲基硅氧烷柱上的保留指数进行了测定和定性确认。根据GC-MS定性分析结果建立了MTO副产汽油中C5~C7烯烃的保留指数数据库,采用气相色谱对副产汽油中C5~C7烯烃组分进行了定量分析。定量结果表明:MTO汽油以C5~C7脂肪族烯烃为主,含有少量的二烯烃和环烯烃,烷烃和环烷烃含量很少。MTO副产汽油中C5~C7烯烃的详细表征为其综合利用提供了依据。     

Tetraphosphine/palladium-catalyzed Heck reactions of aryl halides with disubstituted alkenes

cis,cis,cis-1,2,3,4-Tetrakis(diphenylphosphinomethyl)cyclopentane/[PdCl(C₃H₅)]₂ efficiently catalyses the Heck reaction of disubstituted alkenes such as methyl crotonate, ethyl cinnamate, methyl methacrylate or α-methylstyrene with a variety of aryl halides. In the presence of 1,2-disubstituted alkenes the stereoselectivities of the reactions strongly depend on the substituents of the alkenes. Selectivities up to 97% in favor of E-isomers can be obtained for the addition to methyl crotonate. With the 1,1-disubstituted alkenes methyl methacrylate or α-methylstyrene mixtures of products are obtained.     

Palladium-catalyzed aziridination of alkenes using N,N-dichloro-p-toluenesulfonamide as nitrogen source

N,N-Dichloro-p-toluenesulfonamide (TsNCl₂) was found to be an efficient nitrogen source for the aziridination of unfunctionalized alkenes using palladium catalysts. Among the palladium salts, palladium acetate was the most effective catalyst for this reaction. A variety of alkenes were reacted at room temperature with TsNCl₂ to form the desired aziridines in moderate to good yields. This method can complement our previous protocol which is limited to the use of electron-deficient α,β-unsaturated alkenes.     

Reaction of alkenes and dienes with t-butylmagnesium halides and zirconocene dihalides. A convenient procedure for hydrozirconation and a novel t-butylzirconation of conjugated alkenes

The reaction of nonconjugated monosubstituted alkenes with t-BuMgCl and Cl₂ZrCp₂ at room temperature produces the corresponding monoalkylzirconium derivatives in high yields, while conjugated alkenes undergo either a novel t-butylzirconation or hydrozirconation depending on the reaction conditions.     

Tributylphosphine catalyzed addition of diphenylphosphine oxide to unsubstituted and substituted electron-deficient alkenes

The PBu₃-catalyzed conjugate addition of diphenylphosphine oxide to unsubstituted and substituted electron-deficient alkenes is reported. β-Substituted α,β-unsaturated esters, trans-methyl crotonate and trans-methyl cinnamate, known for their reluctance to participate in phosphine-catalyzed transformations, also react well under the developed conditions. Mild reaction conditions, simple work-up and the ease of catalyst recovery make the proposed methodology useful for the preparation of functionalized tertiary phosphine oxides. The utility of this method was demonstrated by the gram-scale reactions of diphenylphosphine oxide with electron-deficient alkenes.     

Ruthenium-catalyzed addition of sulfenamides to alkynes leading to selective synthesis of polyfunctional alkenes

Sulfenamides smoothly add to alkynes by [RuCl₂(CO)₃]₂ or Ru₃(CO)₁₂ catalyst to give the corresponding polyfunctional alkenes in high yield with high regio- and stereoselectivity (Z 100%).     

Synthesis and N-functionalization of isoxazolidines: a new approach to nucleoside analogues

A straightforward synthetic approach for the preparation of non N-functionalized isoxazolidines from BF₃-catalyzed 1,3-cycloaddition reactions between methyl glyoxylate oxime and alkenes is described. Subsequently, isoxazolidines were N-functionalized with three chemically active groups (2-chloroethyl, cyanomethyl and 2-acetoxyethyl), thus allowing the preparation of a wide array of N-functionalized isoxazolidines. The compounds were characterized by means of ¹H and ¹³C NMR spectroscopy and mass spectrometry. X-ray analysis was used for stereochemical elucidation.     

Isomerization of alkenes in the presence of Pd(acac)2-BF3OEt2 catalytic system

Positional isomerization of alkenes was studied in the presence of Pd(acac)₂ + 20BF₃OEt₂ catalytic system. The reactivity of alkenes decreases in the following order: 1-hexene > 1-heptene > 2-methyl-1-pentene > 4-methyl-2-pentene (cis + trans).     

The catalysis of alkene isomerisation,oligomerisation, and polymerisation by cationic nitrosylrhodium complexes

The complex [Rh(NO)(NCMe)₄][BF₄]₂ catalyses the isomerisation of terminal to internal alkenes, the oligomerisation of branched alkenes such as 2-methylpropene, and the stereospecific polymerisation of buta-1,3-diene to trans-1,4-polybutadiene.     

Osmium-catalyzed dihydroxylation of alkenes by H2O2 in room temperature ionic liquid co-catalyzed by VO(acac)2 or MeReO3

Room temperature ionic liquid [bmim]PF₆ was used to immobilize a bimetallic catalytic system for H₂O₂-based dihydroxylation of alkenes. Osmium tetroxide was used as the substrate-selective catalyst with either VO(acac)₂ or MeReO₃ as co-catalyst. The latter serve as an electron transfer mediator (ETM) and activates H₂O₂. For an increased efficiency N-methylmorpholine is required as an additional ETM in most cases. A range of alkenes were dihydroxylated using this robust bimetallic system and it was demonstrated that for some of the alkenes the catalytic system can be recycled and used up to five times.     

Neutral and cationic (pyrazolylmethyl)pyridine palladium(II) complexes: kinetics and chemoselectivity studies in hydrogenation of alkenes and alkynes

Reactions of (3,5-dimethylpyrazolylmethyl)pyridine (L1) and (3,5-diphenylpyrazolylmethyl)pyridine (L2) with either [PdCl₂(NCMe)₂] or [PdClMe(COD)] afforded the respective neutral palladium complexes, [PdCl₂(L1)] (1), [PdCl₂(L2)] (2) and [PdClMe(L1)] (3). Treatment of complex 1 with equimolar amounts of PPh₃ or PPh₃/NaBAr₄ produced the corresponding cationic complexes [Pd(L1)ClPPh₃]Cl (4) and [Pd(L1)ClPPh₃]BAr₄ (5), respectively. Complexes 1–5 formed active catalysts in hydrogenation of alkenes and alkynes. Isomerization reactions were predominant in the hydrogenation reactions of terminal alkenes, while hydrogenation of alkynes involved a two-step process via alkene intermediates prior to the formation of the respective alkenes. The lack of induction periods in the hydrogenation reactions in addition to pseudo-first-order kinetics with respect to the substrates established the homogeneous nature of the active species.     

Metal triflate catalyzed highly regio- and stereoselective 1,2-bromoazidation of alkenes using NBS and TMSN3 as the bromine and azide sources

Metal triflate catalyzed 1,2-bromoazidation of alkenes was performed using N-bromosuccinimide (NBS) and trimethylsilyl azide (TMSN₃) as the bromine and azide sources, respectively. Among the metal triflates, Zn(OTf)₂ was found to be the best catalyst. This catalytic process represents a highly regioselective, stereoselective and high yielding method for the synthesis of anti-1,2-bromoazides from a variety of alkenes including α,β-unsaturated carbonyl compounds.