Iron(III) porphyrin catalyzed aziridination of alkenes with bromamine-T as nitrene source

[reaction: see text] Iron(III) porphyrin complexes Fe(Por)Cl are effective catalysts for aziridination of alkenes using bromamine-T as the nitrene source. The catalytic system can operate under mild conditions with alkenes as limiting reagents. The aziridination reaction is general and suitable for a wide variety of alkenes, including aromatic, aliphatic, cyclic, and acyclic olefins, as well as alpha,beta-unsaturated esters. For 1,2-disubstituted olefins, the reactions proceeded with moderate to low stereospecificity.     

Practical olefin aziridination with a broad substrate scope.

The present study illustrates the possibility of a rational approach that bypasses the requirement for stoichiometric amounts of toxic oxidants and metal additives (including reagents and catalysts) in organic redox reactions. We describe an aziridination process that delivers a nitrene functionality to olefins from a readily available N-aminophthalimide. Remarkably, both electron-rich and electron-poor olefins are converted to aziridines with high efficiency. The continuum of applied potentials and the heterogeneous nature of reactions at electrode surfaces allow for the electrochemical discrimination of substrates which have similar redox potentials and therefore cannot be selectively reduced or oxidized using soluble reagents. This selectivity is due to the phenomenon of overpotential, the kinetic inhibition of electron transfer on a particular electrode surface.     

Photopromoted Methoxycarbonylation of Olefins Under Ambient Conditions in DMF

Photopromoted methoxycarbonylation of olefins with carbon monoxide can be carded out under ambient conditions with non-precious transition metal complexes (such as cobalt complexes) catalysts in DME The isotope experiments show that DMF is decomposed under irradiation and is conveniently used as a carbon monoxide source for the reaction.     

金属配合物催化氮杂环丙烷化和饱和C-H键氮插入反应

氮杂环丙烷是有机合成之砌块,其合成方法是重要的研究课题.本文全面介绍了近20年来的氮杂环丙烷的金属配合物催化合成,尤其是以氮宾转移到烯烃或碳宾加成到亚胺 为合成途径的氮杂环丙烷化催化反应的研究进展,还包括该反应在金属催化时发生的竞争性插入到饱和C-H键的反应.     

One-pot enantioselective aziridination of olefins catalyzed by a copper(I) complex of a novel diimine ligand by using PhI(OAc)(2) and sulfonamide as nitrene precursors

A novel chiral C(2)-symmetric 1,4-diamine with multistereogenic centers at the backbone of the ligand has been synthesized from cheap natural product D-mannitol through multistep transformations. Its diimine derivative (3 a) was found to be highly effective for the enantioselective control of the copper-catalyzed asymmetric aziridination of olefin derivatives with PhI==NTs as the nitrene source, affording the corresponding N-sulfonylated azirindine derivatives in good to excellent yields with up to 99 % ee (ee=enantiomeric excess). The catalyst system discovered in the present work was also extended to a one-pot enantioselective aziridination by using sulfonamide/iodobenzene diacetate as the nitrene source. In this case, most reactions proceeded smoothly to give the corresponding products in moderate yields with good to excellent enantiomeric excesses (75-96 % ee).     

氮杂环丙化反应研究的新近进展

综述了近几年氮杂环丙化反应研究工作的进展, 重点介绍了乃春与烯烃的转换, 卡宾与N＝C的转换以及不同反应底物官能团转换的合成策略.     

Spin‐Selective Generation of Triplet Nitrenes: Olefin Aziridination through Visible‐Light Photosensitization of Azidoformates

Azidoformates are interesting potential nitrene precursors, but their direct photochemical activation can result in competitive formation of aziridination and allylic amination products. Herein, we show that visible‐light‐activated transition‐metal complexes can be triplet sensitizers that selectively produce aziridines through the spin‐selective photogeneration of triplet nitrenes from azidoformates. This approach enables the aziridination of a wide range of alkenes and the formal oxyamination of enol ethers using the alkene as the limiting reagent. Preparative‐scale aziridinations can be easily achieved under continuous‐flow conditions.     

Iron porphyrin catalysed light driven C–H bond amination and alkene aziridination with organic azides

Visible light driven nitrene transfer and insertion reactions of organic azides are an attractive strategy for the design of C–N bond formation reactions under mild reaction conditions, the challenge being lack of selectivity as a free nitrene reactive intermediate is usually involved. Herein is described an iron(iii) porphyrin catalysed sp³ C–H amination and alkene aziridination with selectivity by using organic azides as the nitrogen source under blue LED light (469 nm) irradiation. The photochemical reactions display chemo- and regio-selectivity and are effective for the late-stage functionalization of natural and bioactive compounds with complexity. Mechanistic studies revealed that iron porphyrin plays a dual role as a photosensitizer and as a catalyst giving rise to a reactive iron–nitrene intermediate for subsequent C–N bond formation.

An iron(iii) porphyrin catalysed sp³ C–H amination and alkene aziridination with broad substrate scope under mild conditions is conducted, with selectivity through the use of organic azides as the nitrogen source under blue LED light irradiation.     

金属络合物催化剂在不对称氮杂环丙烷反应中的研究进展

不对称氮杂环丙烷化;手性催化;金属络合物催化剂在不对称氮杂环丙烷反应中的研究进展     

Cobalt-catalyzed aziridination with diphenylphosphoryl azide (DPPA): direct synthesis of N-phosphorus-substituted aziridines from alkenes

A new catalytic aziridination system that consists of cobalt(II) tetraphenylporphyrin [Co(TPP)] as the catalyst and diphenylphosphoryl azide (DPPA) as the nitrene source has been developed. The cobalt-based catalytic system allows direct synthesis of N-phosphorus-substituted aziridines from alkenes with dinitrogen as the byproduct. Cobalt ion seems essential to the catalytic aziridination with DPPA as no or only trace amounts of the desired products were observed with other metal complexes of tetraphenylporphyrin.     

Catalyst-Controlled Chemoselective Nitrene Transfers

Transition metal catalyzed nitrene transfers provide nitrogen containing compounds through C−H bond insertion, aziridination of olefins, and other types of reactions. Given the importance of these compounds in natural products and pharmaceuticals, tremendous efforts have been devoted to the development of efficient and reliable catalytic methods. In particular, the last decade has seen a remarkable progress in catalyst-controlled chemoselective nitrene transfers, wherein different products can be obtained from a single substrate by the choice of catalyst. This Minireview covers this important and emerging area. We explain the principle of catalyst-controlled synthesis, followed by highlighting literature examples for intra- and intermolecular reactions with an emphasis on the understanding of the nature of reactive intermediates and the strategy needed to realize selectivity. Finally, future directions are discussed based on the literature precedents.     

Sodium Benzoate as a Green,Efficient, and Recyclable Catalyst for Knoevenagel Condensation

Sodium benzoate was utilized as a novel efficient and green catalyst for the Knoevenagel condensation of aldehydes with active methylene compounds such as ethyl cyanoacetate and malononitrile to afford substituted olefins through the conventional stirring or under ultrasounic irradiation. Improvements were observed by carrying out the reactions under ultrasound irradiation. The reaction proceeded smoothly under mild conditions at room temperature, and the products were obtained in excellent yields within short times: The catalyst remains active and exhibits no substantial loss of activity for up to four reaction cycles.     

Copper(I)-catalyzed asymmetric alkene aziridination mediated by PhI(OAc)2: a facile one-pot procedure

A facile one-pot procedure for copper-catalyzed PhI(OAc)₂-mediated asymmetric alkene aziridination had been developed. Commercially available PhI(OAc)₂ and sulfonamides were used to generate the nitrene precursors (PhINR) in situ for olefin aziridination. This one-pot procedure had been optimized using 4-nitrobenzenesulfonamide as the nitrene source. With 5 mol % of the chiral copper catalyst, these conditions afforded 94% yield of the isolated product with 75% ee. We had also developed a simple and rapid method to monitor the rate of this one-pot aziridination.     

Synthesis,Structure, and Highly Efficient Copper‐Catalyzed Aziridination with a Tetraaza‐Bispidine Ligand

The distorted trigonal‐bipyramidal Cu^II complex [Cu(L¹)(NCCH₃)]²⁺ of the novel tetradentate bispidine‐derived ligand L¹ with four tertiary amine donors (L¹=1,5‐diphenyl‐3‐methyl‐7‐(1,4,6‐trimethyl‐1,4‐diazacycloheptane‐6‐yl)diazabicyclo[3.3.1]nonane‐9‐one) is a very efficient catalyst for the aziridination of olefins in the presence of a nitrene source. In agreement with the experimental data (in situ spectroscopy, product distribution, and its dependence on the geometry of the substrate and of the nitrene source), a theoretical analysis based on DFT calculations indicates that the active catalyst has the Cu center in its +II oxidation state, that electron transfer is not involved, and that the conversion of the olefin to an aziridine is a stepwise process involving a radical intermediate. The striking change of efficiency and reaction mechanism between classical copper–bispidine complexes and the novel L¹‐based catalyst is primarily attributed to the structural variation, enforced by the ligand architecture.     

手性双唑啉铜配合物在不对称合成中的应用

综述了手性双E唑啉配体的主要结构类型,并讨论了手性双E唑啉铜配合物在不对称Diels-Alder反应、Ene反应、Mukaiyama adol反应、烯丙基氧化、环丙烷化、氮杂环丙烷化等反应中的应用。     

Aziridination of styrene: comparison of [N-(p-tolylsulfonyl)imino]phenyliodinane and chloramine-T as nitrene donors

Chloramine-T and [N-(p-tolylsulfonyl)imino]phenyliodinane (PhI=NTs) are contrasted as nitrene donors for the aziridination of styrene using copper(II) triflate, and copper-exchanged zeolite Y (CuHY) as catalysts. For both catalysts, PhI=NTs is found to give significantly higher yields of the aziridine both in the presence and absence of a chiral bis(oxazoline) modifier. In addition, chloramine-T is found to induce leaching of most of the Cu from CuHY, and with this nitrene donor CuHY does not function as a heterogeneous catalyst. In contrast, PhI=NTs causes negligible leaching of Cu from CuHY and, consequently, for the heterogeneous CuHY catalyst, PhI=NTs is the preferred nitrene donor. With chloramine-T, the beneficial effects observed on addition of copper powder are shown to be due to the copper powder acting as a reservoir for Cu²⁺ in solution, since Cu²⁺ in solution is rapidly deactivated by toluenesulfonamide, a degradation product of the nitrene donor.     

Copper(II) Triflate Catalyzed Amination of 1,3‐Dicarbonyl Compounds

A method to prepare α,α‐acyl amino acid derivatives efficiently by Cu(OTf)₂+1,10‐phenanthroline (1,10‐phen)‐catalyzed amination of 1,3‐dicarbonyl compounds with PhI?NSO₂Ar is described. The mechanism is thought to initially involve aziridination of the enolic form of the substrate, formed in situ through coordination to the Lewis acidic metal catalyst, by the putative copper–nitrene/imido species generated from the reaction of the metal catalyst with the iminoiodane source. Subsequent ring opening of the resultant aziridinol adduct under the Lewis acidic conditions then provided the α‐aminated product. The utility of this method was exemplified by the enantioselective synthesis of a precursor of 3‐styryl‐2‐benzoyl‐L ‐alanine.     

Aziridination of alkenes using N-iodo-N-potassio-p-toluenesulphonamide as a nitrene precursor

N-Iodo-N-potassio-p-toluenesulphonamide was found to be a convenient nitrene precursor for the aziridination of alkenes in the presence of copper catalysts.     

Bonding and structure of copper nitrenes

Copper nitrenes are of interest as intermediates in the catalytic aziridination of olefins and the amination of C-H bonds. However, despite advances in the isolation and study of late-transition-metal multiply bonded complexes, a bona fide structurally characterized example of a terminal copper nitrene has, to our knowledge, not been reported. In anticipation of such a report, terminal copper nitrenes are studied from a computational perspective. The nitrene complexes studied here are of the form (beta-diketiminate)Cu(NPh). Density functional theory (DFT), complete active space self-consistent-field (CASSCF) electronic structure techniques, and hybrid quantum mechanical/molecular mechanical (QM/MM) methods are employed to study such species. While DFT methods indicate that a triplet (S = 1) is the ground state, CASSCF calculations indicate that a singlet (S = 0) is the ground state, with only a small energy gap between the singlet and triplet. Moreover, the ground-state (open-shell) singlet copper nitrene is found to be highly multiconfigurational (i.e., biradical) and to possess a bent geometry about the nitrene nitrogen, contrasting with the linear nitrene geometry of the triplet copper nitrenes. CASSCF calculations also reveal the existence of a closed-shell singlet state with some degree of multiple bonding character for the copper-nitrene bond.     

NBS‐Mediated Aziridination between Styrenes and Amides under Transition Metal‐Free Conditions

An efficient and simple protocol for N‐bromosuccinimide (NBS)‐mediated styrenes aziridination using amides as the nitrenoid source has been developed. This aziridination affords desired products in moderate to good yields without using transition metal catalyst under very mild reaction condition.