Asymmetric N1 unit transfer to olefins with a chiral nitridomanganese complex: novel stereoselective pathways to aziridines or oxazolines

Chiral nitridomanganese complex 1 was found to be a highly potential N1 unit source for the asymmetric synthesis of aziridines and 2-oxazolines from olefins such as styrene and its derivatives. When sulfonyl chlorides were employed as activators of the complex in the presence of pyridine, pyridine N-oxide, and a silver salt, the reaction of olefins with complex 1 proceeded smoothly to afford the N-sulfonylated aziridines. The aziridination of styrene derivatives with complex 1 using 2-trimethylsilylethanesulfonyl chloride (SESCl) gave the N-SES-aziridines, which were easily converted into chiral N-unsubstituted aziridines. It was found that the reaction was applicable to the asymmetric synthesis of 2-oxazolines from olefins when acyl chlorides were employed as activators. Complex 1 provided an effective asymmetric environment for trans-disubstituted styrenes in the reaction (up to 92% ee). This is the first example of a direct asymmetric synthesis of 2-oxazolines from olefins. Additional experiments, conducted during the course of this investigation, suggest that the isomerization of the N-acylaziridine intermediate is involved in this reaction.     

Intramolecular Aminoboration of Unfunctionalized Olefins

A direct and catalyst‐free method for the intramolecular aminoboration of unfunctionalized olefins is reported. In the presence of BCl₃ (1 equiv) as the sole boron source, intramolecular aminoboration of sulfonamide derivatives of 4‐penten‐1‐amines, 5‐hexen‐1‐amines, and 2‐allylanilines proceeded readily without the use of any catalyst. The boronic acids obtained after hydrolysis could be converted into the corresponding pinacol borates in a straightforward manner by treatment with pinacol under anhydrous conditions.     

Synthesis of monohalocyclopropane derivatives from olefins by the reaction with trihalomethanes and copper

Fluoro-, chloro-, bromo-, and iodocyclopropane derivatives were obtained in 10–80% yields by the reaction of FCHI₂, ClCHI₂, BrCHI₂, and CHI₃, respectively, with Cu in the presence of olefins. The reaction was electrophilic, and proceeded stereospecifically, i.e., cis and trans olefins afforded cyclopropane derivatives whose configurations with respect to the substituents from original olefins were cis and trans, respectively. Since isomeric olefins were not detected in the reaction mixture which would be expected from the insertion of the corresponding free monohalocarbenes into C—H bonds, the reaction seemed to proceed via organocopper intermediates rather than free monohalocarbenes. With respect to the configuration of the halogen introduced by the new reaction, the cis or endo isomers were generally obtained predominantly over the corresponding trans or exo isomers.     

Zirconium-mediated intramolecular ester transfer reaction: synthesis of alpha-substituted gamma-aminobutyric acid (GABA) derivatives

[reaction: see text]. The zirconium-mediated intramolecular ester transfer reaction of N-alkenyl carbamate derivatives proceeded to give alpha-substituted gamma-aminobutyric acid (GABA) derivatives in good to excellent yields. Quenching experiments of the reaction mixture with iodine or O2 indicated the presence of a cyclopropane intermediate. The resulting iodide was converted to 2-substituted pyrrolidine-3-carboxylate and/or alpha-alkylidene-gamma-aminobutyric acid derivatives in a stereospecific manner.     

Catalytic oxidative cleavage of terminal olefins by chromium(III) stearate

A new synthetic methodology for the preparation of carbonyl compounds from the oxidative cleavage of terminal olefins has been developed. With the use of TBHP in combination with chromium(III) stearate, selective oxidation of double bonds conjugated with aromatic ring or carbonyl group could be achieved at ambient temperature in moderate to excellent yield. The oxidative cleavage of electron rich -methylstyrene derivatives proceeded in good to excellent yield whereas lower yields were observed in -methylstyrene derivatives containing an electron withdrawing group. This developed oxidation reaction was believed to undergo via free radical process and high valent chromium oxo species.     

Copper-catalyzed ortho-Monofluorination of Aniline Derivatives with Selectfluor Directed by Picolinic Acid Amides

A novel and facile method for selective ortho-C-H monofluorination of aniline derivatives was achieved using Selectfluor/Cu(OAc)₂/HOAc system. The reaction proceeded via electrophilic process with diverse substrates in acceptable moderate to high yields. The position selectivity was controlled by bidentate coordination of picolinic acid amides with copper.     

Efficient copper-catalyzed benzylic amidation with anhydrous chloramine-T

Benzylic hydrocarbons are selectively converted to the corresponding sulfonamides by the [Cu(CH(3)CN)(4)]PF(6)-catalyzed reaction with anhydrous TolSO(2)NNaCl (chloramine-T). Under the same conditions, representative ethers are also alpha-amidated; olefins produce allyl sulfonamides, aziridines, and/or beta-chloro sulfonamides.     

Highly efficient solid-phase oxidative cleavage of olefins by OsO4-NalO4 in the intramolecular N-acyliminium Pictet-Spengler reaction

[reaction: see text] In the present investigation, solid-supported peptide olefins were converted quantitatively to aldehydes via the OsO(4)-NaIO(4)-mediated oxidative cleavage reaction. Addition of DABCO was essential to efficiently suppress the formation of hydroxymethyl ketone side products. The generated aldehydes were used in intramolecular N-acyliminium Pictet-Spengler reactions to produce highly pure pyrroloisoquinoline derivatives. The methodology was extended to allylglycine derivatives to enable the incorporation of pyrroloisoquinoline scaffolds within peptides.     

Synthesis of functionalized iodoalkenes using a multicomponent reaction triggered by electrophilic iodination of alkenyldiazoacetates

Diazo compounds are frequently used as precursors of metal carbenoids and act as soft nucleophiles even without the use of metal catalysts. The resulting diazonium species may also be trapped by various nucleophiles. The introduction of an iodine functionality applicable for the coupling reaction into an alkenyl diazo compound, however, has not been reported. We developed iodoalkoxylation reactions of alkenyl diazoacetates using an electrophilic iodinating reagent and oxygen nucleophile. This catalyst-free multicomponent reaction proceeded regioselectively, furnishing trisubstituted vinyl iodides in 31%–71% yield. The synthesized iodoalkenes were converted into the corresponding olefins with various functionalities in good yield via Suzuki-Miyaura coupling reactions with arylboronic acids under palladium catalysis to demonstrate the synthetic utility of the developed reaction sequence.     

Catalytic Asymmetric Synthesis of α-Quaternary Proline Derivatives by 1,3-Dipolar Cycloaddition of α-Silylimines

Going pro: The title reaction between α-silylimines and activated olefins proceeds in the presence of a Cu(I) /DTBM-Segphos catalyst system with excellent diastereoselectivity and enantioselectivity. This process provides straightforward access to highly enantioenriched 5-unsubstituted α-quaternary proline derivatives. TMS=trimethylsilyl, DTBM-Segphos=5,5'-bis[di(3,5-di-tert-butyl-4-methoxyphenyl)phosphino]-4,4'-bi-1,3-benzodioxole.     

Chlorination of oximes in hydrogen fluoride: formation of gem-dihalogenoalkanes

The action of chlorine on oximes in hydrogen fluoride as a medium gives gem-dihalogenoalkanes. The reaction proceeds through the intermediate formation of gem-chloronitrosoalkanes. The relative proportions between gem-dichloro, -difluoro and -fluorochloro compounds are dependent on the presence of a cosolvent. The use of other oxidants, such as nitric oxide, dinitrogen tetroxide or nitrosyl chloride, gives similar compounds.     

Chiral Silver Amides as Effective Catalysts for Enantioselective [3+2] Cycloaddition Reactions

Asymmetric [3+2] cycloaddition of α‐aminoester Schiff bases with substituted olefins is one of the most efficient methods for the preparation of chiral pyrrolidine derivatives in optically pure form. In spite of its potential utility, applicable substrates for this method have been limited to Schiff bases that bear relatively acidic α‐hydrogen atoms. Here we report a chiral silver amide complex for asymmetric [3+2] cycloaddition reactions. A silver complex prepared from silver bis(trimethylsilyl)amide (AgHMDS) and (R)‐DTBM‐SEGPHOS worked well in asymmetric [3+2] cycloaddition reactions of α‐aminoester Schiff bases with several olefins to afford the corresponding pyrrolidine derivatives in high yields with remarkable exo‐ and enantioselectivities. Furthermore, α‐aminophosphonate Schiff bases, which have less acidic α‐hydrogen atoms, also reacted with olefins with high exo‐ and enantioselectivities. The stereoselectivities of the [3+2] cycloadditions with maleate and fumarate suggested that the reaction proceeded by means of a concerted mechanism. An NMR spectroscopic study indicated that complexation of AgHMDS with the bisphosphine ligand was not complete, and that free AgHMDS, which did not show any significant catalytic activity, existed in the catalyst solution. This means that significant ligand acceleration occurred in the current reaction system.     

由α-氰基肉桂酸乙酯/N-溴代苯甲酰胺合成2-噁唑啉衍生物

作为重要的杂环化合物,合成新的2-噁唑啉衍生物以及发展其新的合成方法具有重要意义,为此以α-氰基肉桂酸乙酯衍生物为底物,以N-溴苯甲酰胺为反应试剂,在无水碳酸钠(相对于底物3为110%摩尔分数)促进下,在丙酮溶剂中,室温下,建立了合成相应2-噁唑啉衍生物的新方法,共合成了11个新化合物,其结构由核磁共振波谱仪(~1H NMR,~(13)C NMR)和高分辨质谱(HRMS)确认。结果显示,各种α-氰基肉桂酸乙酯衍生物(3a~3k)可被顺利的转化成相应的2-噁唑啉衍生物(5a~5k)。在室温下,丙酮作溶剂,以Na_2CO_3为促进剂时,相应产物的最高收率可达90%。不仅α-氰基肉桂酸乙酯衍生物(3)可被用作该反应的底物,而且α-乙氧甲酰基肉桂酸乙酯(6)也适用于该反应。实验结果还证明,除了N-溴代苯甲酰胺外,N-溴代对硝基苯甲酰胺(8)及N-溴代乙酰胺(9)也适用该反应,证明该方法具有广泛的适应性。根据实验结果,提出了可能的反应机理,该机理支持了形成2-噁唑啉衍生物的区域选择性。     

Highly diastereoselective approach toward (+/-)-tetraponerine T6 and analogues via the double cycloisomerization-reduction of bis-alkynylpyrimidines

A new, short, and efficient approach toward tricyclic alkaloids, involving the double cycloisomerization-reduction of bis-alkynylpyrimidines 3a-m, has been developed. The requisite bis-alkynylpyrimidines 3a-m were readily prepared via regioselective sequential Sonogashira coupling reactions of dibromopyrimidines 1. Bis-alkynylpyrimidines 3a-m were converted into the 5-6-5 tricyclic heteroaromatic cores 4a-m via the Cu(I)-assisted double cycloisomerization reaction. The reaction proceeded stepwise, which was confirmed by the isolation of the mono-pyrrolization intermediate 5. The structure of 5 was assigned by 2D NMR and by independent synthesis. Cycloisomerization of 5 under standard conditions afforded tricyclic 4g in 89% yield. The PtO2-catalyzed hydrogenation of bis-pyrrolopyrimidines 4d, 4g, and 4i in acidic media afforded stable amidinium derivatives, 11a, 11b, and 11c. Further reduction of the latter with LiAlH4 allowed for the highly diastereoselective total synthesis of (+/-)-tetraponerine T6 and its analogues.     

Copper(I)-catalyzed reaction of acylzirconocene chloride: cross-coupling and conjugate addition

For the purpose of exploring a new reaction of acylzirconocene chloride as an acyl anion donor, Cu(I)-catalyzed cross-coupling and conjugate addition reactions of acylzirconocene chloride were studied. The coupling reaction with allylic or propargylic halides efficiently proceeded to yield β,γ-unsaturated ketone or allenyl ketone derivatives, respectively. The conjugated addition reaction to ,β-enones was carried out in the presence of 2 equiv. of BF₃·OEt₂ giving 1,4-diketone compounds.     

Reversible modification of oligodeoxynucleotides: click reaction at phosphate group and alkali treatment

We characterized click reaction between oligodeoxynucleotides (ODNs) possessing acetylene groups at the phosphate unit and azide compounds. Cu(I)-catalyzed cycloaddition proceeded efficiently to form the corresponding functional ODNs. The resulting ODNs could be converted into ordinary ODNs by treatment with aqueous methylamine. The present method successfully achieved a reversible modification of ODNs.     

The combination of benzamides/NCS as nitrogen/halogen sources for aminohalogenation of β-nitrostyrenes resulting in dichlorinated haloamides

The combination of benzamide and NCS was found to be an efficient nitrogen/halogen source for aminohalogenation of β-nitrostyrenes. The reaction was convenient to carry out by using 4-dimethylaminopyridine as the catalyst, resulting in vicinal dichlorinated haloamino nitroalkanes with opposite regiochemistry to that generated from other electron-deficient olefins observed previously. The reaction proceeded smoothly at room temperature with good yields and excellent regioselectivities. A mechanism involving a chloronium intermediate was proposed to explain the resulting regiochemistry. The current system explored a new type of nitrogen sources for aminohalogenation of functionalized olefins.     

Effect of acid density of HZSM-5 on the oligomerization of ethylene in FCC dry gas

The oligomerization of ethylene in FCC dry gas over HZSM-5 catalyst with different Si/Al2 ratios was studied. The effect of acid density of catalyst on the oligomerization of ethylene was discussed. By increasing the acid density of catalyst, ethylene conversion showed a linear increase, while the yields of olefins decreased when the acid density of catalyst exceeded 0.14 mmolNH3/g owing to a promotion of hydrogen transfer reaction. Through comparing the average distance between acid sites on catalyst with kinetic diameters of olefins, it was found that the dimerization of ethylene was not restrained by the sparse distribution of acid sites, while the hydrogen transfer reaction of C3 and C4 olefins was limited. On these bases, a conclusion is proposed that the dimerization of ethylene proceeded via Eley-Rideal mechanism, while the hydrogen transfer reaction of C3 and C4 olefins followed the Langmuir-Hinshelwood mechanism.     

Radiolabeling and biodistribution of 62Cu-dithiocarbamate--an application for the new 62Zn/62Cu generator

The newly developed 62Zn/62Cu generator system has made available the production of the short-lived 62Cu (T1/2 = 9.8 min) positron radionuclide, eluted as 62Cu-glycine. In the search for 62Cu labeled radiopharmaceuticals for positron CT (PET) brain diagnostic studies, two ligands N,N-diethyl- and N,N-dimethyl-dithiocarbamic acid (DDC and DmDC) were selected, based on their Cu chelating abilities and the neutral lipophilic character of their copper chelates. In the present work, an in vitro study with non-radioactive Cu-glycine showed that both ligands easily formed the stable, neutral Cu-DDC and Cu-DmDC chelates (1:2 metal-ligand complexes) based on the ligand exchange reaction. Then the 62Zn/62Cu generator eluate, the 62Cu-glycine was used for the radiolabeling of DDC and DmDC. The following HPLC analysis revealed that the ligand exchange reaction proceeded rapidly; the radiochemical purities of 62Cu-DDC and 62Cu-DmDC were extremely high (non-detectable 62Cu-glycine) and both chelates were more lipophilic than 62Cu-glycine. The mouse biodistribution of both radiolabeled compounds, 62Cu-DDC and 62Cu-DmDC indicated a brain accumulation of 2.8 and 5.3 times higher than 62Cu-glycine, 15 min post injection, respectively. The brain accumulation observed with both 62Cu-DDC and 62Cu-DmDC might be due to their stable, neutral and lipophylic character; the latter enhanced by the presence of the methylated side chains. The gathered results indicated the applicability of dithiocarbamic acid derivatives in the production of new 62Cu-labeled compounds using the 62Zn/62Cu generator system based on the ligand exchange reaction with 62Cu-glycine eluate. Further studies with Cu-dithiocarbamic acid derivatives for development of new generator-produced 62Cu positron radiopharmaceuticals can be recalled.     

Mn(III)acetate-mediated additions of active methylene compounds to bicyclic olefins: Synthesis of bicyclic olefin-fused dihydrofurans

Bicyclic alkenes such as benzonorbornadiene, oxabenzonorbornadiene, norbornene, and norbornadiene were reacted with 1,3-cyclohexanedione and ethyl acetoacetate in the presence of Mn(OAc)₃ and Cu(OAc)₂. Except for the reaction of benzonorbornadiene and ethyl acetoacetate, dihydrofuran derivatives were the only products obtained. The formation of naphthalene derivatives was observed together with dihydrofuran in the aforementioned benzonorbornadiene/ethyl acetoacetate reaction. Additionally, the dihydrofuran product from the addition of ethyl acetoacetate to norbornadiene was slowly converted into epoxide derivative with air. The mechanism for the formation of the products is discussed.