Iron-catalyzed C–H amination and its application in organic synthesis

Transition-metal-catalyzed direct C–H bond amination is an attractive strategy in preparation of nitrogen containing molecules which are common in naturally occurring and pharmaceutically important compounds. Comparing to the precious metals commonly used in this reaction, non-precious metals such as iron are abundant in earth, relatively low toxic, and more biocompatible, which meet the increasing demand for environmentally benign and sustainable chemical processes. In this review, we described the development in iron catalyzed C–H bond amination reactions from historical landmarks to recent achievements, and placed emphasis on their applications in organic synthesis, i.e. natural product synthesis and/or modification.     

Template-directed CH activation: development and application to the total synthesis of 7-episordidin

The development of a template-directed CH activation strategy and its application to the diastereoselective synthesis of (±)-7-episordidin, an aggregation pheromone from the male banana weevil, Cosmopolites sordidus Germar, is reported. The key step of the synthetic route is a regioselective rhodium(II)-catalyzed diazocarbonyl CH activation reaction that simultaneously generates three of the four stereocenters present in the natural product.     

Tetraorganophosphonium and tetraphenylarsonium salts of B5H8− and B6H9−

Eight new quaternary phosphonium or arsonium salts of the polyhedral borane anions B₅H₈⁻ and B₆H₉⁻ have been prepared in order to study the influence of cation size on stability. The salts are, indeed, considerably more stable than those previously prepared, the most stable being the tetraphenylphosphonium and tetraphenylarsonium derivatives. IR and NMR data are reported.     

Reactions of sodium tetrahydroborate with alkyl and aryl halides: A new approach to the synthesis of B3H 8 − and B12H 12 2− anions

A new method for the synthesis of the B₃H ₈ ^? anion based on the reactions of alkyl and aryl halides (C₂H₄Cl₂, C₆H₅CH₂Cl, C₄H₉Br, (C₆H₅)₃CCl, C₁₀H₇CH₂Cl, CH₂I₂, C₂HCl₃) with sodium tetrahydroborate in diglyme was proposed. The method is characterized by high (up to quantitative) yields and easy isolation of the target products, (n-C₄H₉)₄N)[B₃H₈] and Cs[B₃H₈], and also easy preparation of a salt of higher hydroborate anion, B₁₂H ₁₂ ^2? , without multistage purification from impurities of other anions of this series.     

An Isolable Gallium-Substituted Nitrilimine and its Reactivity with B−H,Si−H and B−B Bonds

Reaction of the Ga(I) compound NacNacGa ( 9 ) with the diazo compound N₂CHSiMe₃ affords the nitrilimine compound NacNacGa(N-NCSiMe₃)(CH₂SiMe₃) ( 10 ). Carrying out this reaction in the presence of pyridine does not lead to C−H activation on the transient alkylidene NacNacGa=CHSiMe₃ but generates a metallated diazo species NacNacGa(NHN=CHSiMe₃)(CN₂SiMe₃) ( 13 ) that further rearranges into the isonitrile compound NacNacGa(NHN=CHSiMe₃)(N(NC)SiMe₃) ( 15 ). Reactions of 10 with the silane H₃SiPh and the borane HBcat furnished products of 1,3 addition to the nitrilimine moiety NacNacGa{N(ER_n)NCSiMe₃}(CH₂SiMe₃), whereas reaction with the diborane B₂cat₂ gave the product of formal nitrene insertion into the B−B bond. DFT calculations suggest that the interaction of 9 with N₂CHSiMe₃ proceeds through intermediate formation of an alkylidene compound that undergoes CH activation with a second molecule of N₂CHSiMe₃. Insertion into the B−B bond likely proceeds through an initial 1,3-addition of the diborane, followed by boryl migration to the former nitrene center.     

Stereoselective allylation of α-hydroxy aldimines and its application to the formal synthesis of (−)-β-conhydrine

Stereoselective allylation of N-p-methoxyphenyl (PMP)-substituted α-hydroxy aldimines is described. Several Lewis acids (BF₃·OEt₂, SnCl₄, TiCl₄, ZnCl₂, and MgBr₂·OEt₂) were employed to mediate the allylation reactions. The addition of the allyl group generates a new stereocenter and affords the syn vicinal amino alcohol. Formal synthesis of (?)-β-conhydrine (1) was accomplished via syn-selective allyl addition to N-PMP-substituted α-hydroxy aldimine.     

Palladium-Catalyzed Atroposelective Kinetic C−H Olefination and Allylation for the Synthesis of C−B Axial Chirality

The direct C−H functionalization of 1,2-benzazaborines, especially asymmetric version, remains a great challenge. Here we report a palladium-catalyzed enantioselective C−H olefination and allylation reactions of 1,2-benzazaborines. This asymmetric approach is a kinetic resolution (KR), providing various C−B axially chiral 2-aryl-1,2-benzazaborines and 3-substituted 2-aryl-1,2-benzazaborines in generally high yields with excellent enantioselectivities (selectivity (S) factor up to 354). The synthetic potential of this reaction is showcased by late-stage modification of complex molecules, scale-up reaction, and applications.     

Sol–gel synthesis of mesoporous silicas containing albumin and guanidine polymers and its application to the bilirubin adsorption

The organic–inorganic composite materials based on mesoporous silica were synthesized using sol–gel method. The surface area of silicas was modified by bovine serum albumin (BSA) and guanidine polymers: polyacrylate guanidine (PAG) and polymethacrylate guanidine. The mesoporous silicas were characterized by nitrogen adsorption–desorption analysis, Fourier transform infrared spectroscopy, transmission electron microscopy. The obtained materials were used as adsorbents for selective bilirubin removal. It was shown that the structural properties and surface area of modified materials depend on the nature of polymers. Incorporation of polymers in silica gel matrix during sol–gel process leads to the formation of mesoporous structure with high pore diameter and a BET surface area equals to 346 m²/g for SiO₂/BSA and 160 m²/g for SiO₂/PAG. Analysis of adsorption isotherms showed that modification of silica by BSA and guanidine polymers increases its adsorption ability to bilirubin molecules. According to Langmuir model, the maximum bilirubin adsorption capacity was 1.18 mg/g.     

Discovery and application of 6π-azaelectrocyclization to natural product synthesis and synthetic biology

While elucidating the inhibitory mechanism of a hydrolytic enzyme by aldehyde-containing natural product,we discovered a reaction involving a rapid 6π-azaelectrocyclization of azatrienes generated from aldehyde with lysine residues.The electrocyclic reaction of the 1-azatriene system,a cyclization precursor,exhibited a significant substituent effect.Asymmetric chiral piperidine synthesis and a one-pot library synthesis of pyridines on solid-supports were applied to synthesize pyridine/indole alkaloid-type natural product.Additionally,we developed lysine-based labeling and engineering of biomolecules and living cells based on the rapid 6π-azaelectrocyclization.Both labels and oligosaccharide structures were introduced efficiently and selectively into surface lysines under the mild conditions;notable effects of N-glycans on proteins and living cells were visualized for the first time by PET and noninvasive fluorescence imaging.     

Diastereoselective α-alkylation of β-hydroxy sulfoxides and its application to the synthesis of (+)- and (3)-disparlure

α-Alkylation of the dianions of β-hydroxy sulfoxides proceeds with high 1, 2-asymmetric induction to give threo-α-alkyl-β-hydroxy sulfoxides. The utility of the present reaction was demonstrated in the asymmetric synthesis of (+)- and (3)-cis-7, 8-epoxy-2-methyloctadecanes (disparlure).     

Silylene transfer to α-keto esters and application to the synthesis of γ-lactones

Disubstituted α-hydroxy acids have been synthesized by metal-catalyzed silylene transfer to α-keto esters. A range of substituents are tolerated in the transformation with the exception of branched groups at the vinylic position. The α-hydroxy acid products can be converted into γ-lactones using a variety of lactonization conditions.     

Stereoselective cyanation of 4-formyl and 4-imino-β-lactams: application to the synthesis of polyfunctionalized γ-lactams

The stereoselective reaction of 4-oxoazetidine-2-carbaldehydes and their corresponding imines with cyanide-based reagents give β-lactam α-aminonitriles, which are chameleonic building blocks for the controlled synthesis of a variety of new compounds including functionalized γ-lactams, succinimide derivatives, and diamino-lactams derivatives in optically pure form.     

The new synthesis of sulfuryl-bridged triazinane and its selective recognition to SO42−

Research on Chemical Intermediates - A new method has been developed for the synthesis of a cage-like sulfuryl-bridged triazinane molecule HEXS by acidic condensation of a glycoluril analog with...     

Total synthesis of (−)-jaspine B and its 4-epi-analogue from d-xylose

The total synthesis of the HCl salts of (−)-jaspine B ent-1 and its 4-epi-congener ent-4 was accomplished starting from the common template 13 derived from d-xylose. The cornerstone of our synthesis was [3,3]-heterosigmatropic rearrangements, which effectively provided scaffolds with a chiral amino group. A subsequent Wittig olefination installed a C₁₄ alkyl side chain and acid-mediated ring-closing reaction established the tetrahydrofuran core.     

Preparation of SAMS-CMC-CS bipolar membrane and its application in electro-generating FeO 4 2−

The preparation of SAMS-CMC-CS bipolar membrane grafted onto CMC by SAMS was reported. The cross-section view of SAMS-CMC-CS BM were studied by SEM. FT-IR spectrum indicated that SAMS-CMC-CS BM contained-SO ₃ ⁻ ,-COO⁻ and −N=CHR functional groups. Compared with CMC-CS BM, SAMS-CMC-CS BM appears to have better mechanical strength and chemical stability in alkali solution at [OH⁻]≥9.5 mol/L, with a swelling of 55 %. The electrochemical properties of SAMS-CMC-CS BM were also studied. SAMS-CS-CMC BM not only effectively prevented FeO ₄ ²⁻ from diffusing into the cathode chamber, but also played an important role in the supply of OH⁻ consumed during the electro-generated FeO ₄ ²⁻ process.      

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons and its application for the synthesis of diaryl ethers

Electrochemical synthesis of copper nanoparticles on nafion–graphene nanoribbons support for the synthesis of diaryl ethers via Ullmann type coupling is reported. The catalyst showed excellent performance for C–O cross coupling reactions under ligand free condition. The catalyst was characterized by various techniques such as SEM, TEM, XRD, EDX, BET, TGA, and UV spectrophotometry. It was recycled several times without significant loss in its catalytic activity.     

Preparation of PLL-PEG-PLL and its application to DNA encapsulation

With the successful sequencing of Human Genome, it would be possible to cure all diseases by gene ther- apy in the near future. However, one of the major problems in gene therapy is the development of gene vectors. To date, there are two kinds of gene vectors, namely, viral and non-viral gene vectors. Viruses are widely used as vectors in gene therapy, with the trans- fection efficiency being relatively high, but they have the safety problems such as immunogenicity, non- biocompatibility and …     

Total synthesis of Yingzhaosu B and its three diastereoisomers

Yingzhaosu B (1), coexisting with Yingzhaosu A (2) which is an antimalarialprinciple in the traditional Chinese herbal medicine Yingzhao (Artabotrys uncina-tus (L.) Merr.), is a polyhydroxy bisabolene compound. Although its structure wasproposed by Liang and coworkers in 1979, the stereochemistry remained unsettled.From biogenetic viewpoint, it is reasonable to assume that the configuration of 4-Cin Yingzhaosu B is S as that in Yingzhaosu A. Recently, the synthesis of degrada     

A facile synthesis of ω-substituted conjugated polyenones via arsonium salt and its application towards the synthesis of navenone A

In the presence of K₂CO₃, a variety of aldehydes condensed with the arsonium bromide 8 at 0–3°C to give exclusively ω-substituted polyenones 1 in good yields, and the synthesis of navenone A was achieved by this procedure.