Unusual chemical transformations such as three‐component combination and ring‐opening of N‐heterocycles or formation of a carbon–carbon double bond through multiple C–H activation were observed in the reactions of TpMe2‐supported yttrium alkyl complexes with aromatic N‐heterocycles. The scorpionate‐anchored yttrium dialkyl complex [TpMe2Y(CH2Ph)2(THF)] reacted with 1‐methylimidazole in 1:2 molar ratio to give a rare hexanuclear 24‐membered rare‐earth metallomacrocyclic compound [TpMe2Y(μ‐N,C‐Im)(η2‐N,C‐Im)]6 ( 1 ; Im=1‐methylimidazolyl) through two kinds of C–H activations at the C2‐ and C5‐positions of the imidazole ring. However, [TpMe2Y(CH2Ph)2(THF)] reacted with two equivalents of 1‐methylbenzimidazole to afford a C–C coupling/ring‐opening/C–C coupling product [TpMe2Y{η3‐(N,N,N)‐N(CH3)C6H4NHCH?C(Ph)CN(CH3)C6H4NH}] ( 2 ). Further investigations indicated that [TpMe2Y(CH2Ph)2(THF)] reacted with benzothiazole in 1:1 or 1:2 molar ratio to produce a C–C coupling/ring‐opening product {(TpMe2)Y[μ‐η2:η1‐SC6H4N(CH?CHPh)](THF)}2 ( 3 ). Moreover, the mixed TpMe2/Cp yttrium monoalkyl complex [(TpMe2)CpYCH2Ph(THF)] reacted with two equivalents of 1‐methylimidazole in THF at room temperature to afford a trinuclear yttrium complex [TpMe2CpY(μ‐N,C‐Im)]3 ( 5 ), whereas when the above reaction was carried out at 55 °C for two days, two structurally characterized metal complexes [TpMe2Y(Im‐TpMe2)] ( 7 ; Im‐TpMe2=1‐methyl‐imidazolyl‐TpMe2) and [Cp3Y(HIm)] ( 8 ; HIm=1‐methylimidazole) were obtained in 26 and 17 % isolated yields, respectively, accompanied by some unidentified materials. The formation of 7 reveals an uncommon example of construction of a C?C bond through multiple C–H activations. 相似文献
Complexes [Re(CO)3(N‐RIm)3]OTf (N‐RIm=N‐alkylimidazole, OTf=trifluoromethanesulfonate; 1 a – d ) have been straightforwardly synthesised from [Re(OTf)(CO)5] and the appropriate N‐alkylimidazole. The reaction of compounds 1 a – d with the strong base KN(SiMe3)2 led to deprotonation of a central C? H group of an imidazole ligand, thus affording very highly reactive derivatives. The latter can evolve through two different pathways, depending on the nature of the substituents of the imidazole ligands. Compound 1 a contains three N‐MeIm ligands, and its product 2 a features a C‐bound imidazol‐2‐yl ligand. When 2 a is treated with HOTf or MeOTf, rhenium N‐heterocyclic carbenes (NHCs) 3 a or 4 a are afforded as a result of the protonation or methylation, respectively, of the non‐coordinated N atom. The reaction of 2 a with [AuCl(PPh3)] led to the heterobimetallic compound 5 , in which the N‐heterocyclic ligand is once again N‐bound to the Re atom and C‐coordinated to the gold fragment. For compounds 1 b – d , with at least one N‐arylimidazole ligand, deprotonation led to an unprecedented reactivity pattern: the carbanion generated by the deprotonation of the C2? H group of an imidazole ligand attacks a central C? H group of a neighbouring N‐RIm ligand, thus affording the product of C? C coupling and ring‐opening of the imidazole moiety that has been attacked ( 2 c , d ). The new complexes featured an amido‐type N atom that can be protonated or methylated, thus obtaining compounds 3 c , d or 4 c , d , respectively. The latter reaction forces a change in the disposition of the olefinic unit generated by the ring‐opening of the N‐RIm ligand from a cisoid to a transoid geometry. Theoretical calculations help to rationalise the experimental observation of ring‐opening (when at least one of the substituents of the imidazole ligands is an aryl group) or tautomerisation of the N‐heterocyclic ligand to afford the imidazol‐2‐yl product. 相似文献
Asymmetric ring‐opening reactions of N‐Boc‐azabenzonorbornadiene with N‐substituted piperazine nucleophiles in the presence of 5 mol% of [Rh(COD)Cl]2 and 10 mol% of chiral ligand, (R,S)‐PPF‐P‐t‐Bu2, gave the corresponding 1,2‐diamine product in moderate to excellent yields (up to 95%) with reasonable enantiomeric excesses (up to 70% ee). The results showed that the nature of ligands had significant influence on the yields and the enantiomeric excesses. 相似文献
Ring opening reactions of N‐sulfonyl aziridines by primary and secondary amines in silica gel (SG)‐water system were achieved, which provided a mild, practical and environmentally benign method to synthesize mono‐ and bis‐sulfonyl substituted amines. When primary and secondary amines were used in excess, they reacted with N‐sulfonyl aziridines smoothly at room temperature, mainly affording 1:1 ring opening products. Reactions of primary amines with 2 equiv. of aziridines produced 2:1 ring opening products. Some 1:1 products can be cyclized with CS2 to synthesize N‐sulfonyl cyclothioureas also in water. 相似文献
Aziridines can undergo a range of ring-opening reactions with nucleophiles. The regio- and stereochemistry of the products depend on the substituents on the aziridine. Aziridine ring-opening reactions have rarely been used in radiosynthesis. Herein we report the ring opening of activated aziridine-2-carboxylates with [18F]fluoride. The aziridine was activated for nucleophilic attack by substitution of various groups on the aziridine nitrogen atom. Fluorine-18 radiolabelling was followed by ester hydrolysis and removal of the activation group. Totally regioselective ring opening and subsequent deprotection was achieved with tert-butyloxycarbonyl- and carboxybenzyl-activated aziridines to give α-[18F]fluoro-β-alanine in good radiochemical yield. 相似文献
1‐[(1R)‐(1‐Phenylethyl)]‐1‐azoniabicyclo[3.1.0]hexane tosylate was generated as a stable bicyclic aziridinium salt from the corresponding 2‐(3‐hydroxypropyl)aziridine upon reaction with p‐toluenesulfonyl anhydride. This bicyclic aziridinium ion was then treated with various nucleophiles including halides, azide, acetate, and cyanide in CH3CN to afford either piperidines or pyrrolidines through regio‐ and stereoselective ring opening, mediated by the characteristics of the applied nucleophile. On the basis of DFT calculations, ring‐opening reactions under thermodynamic control yield piperidines, whereas reactions under kinetic control can yield both piperidines and pyrrolidines depending on the activation energies for both pathways. 相似文献
Reaction of the bicyclo[1.1.0]tetrasilatetraamide Si4{N(SiMe3)Dipp}4 1 (Dipp=2,6‐diisopropylphenyl) with 5 equiv of the N‐heterocyclic carbene NHCMe4 (1,3,4,5‐tetramethylimidazol‐2‐ylidene) affords a bifunctional carbene‐coordinated four‐membered‐ring compound with a Si=N group and a two‐coordinate silicon atom Si4{N(SiMe3)Dipp}2(NHCMe4)2(NDipp) 2 . When 2 reacts with 0.25 equiv sulfur (S8), two sulfur atoms add to the divalent silicon atom in plane and perpendicular to the plane of the Si4 ring, which confirms the silylone character of the two‐coordinate silicon atom in 2 . 相似文献
Nucleophilic ring‐opening reactions of 3‐aryl‐1‐benzylaziridine‐2‐carboxylates were examined by using O‐nucleophiles and aromatic C‐nucleophiles. The stereospecificity was found to depend on substrates and conditions used. Configuration inversion at C(3) was observed with O‐nucleophiles as a major reaction path in the ring‐opening reactions of aziridines carrying an electron‐poor aromatic moiety, whereas mixtures containing preferentially the syn‐diastereoisomer were generally obtained when electron‐rich aziridines were used (Tables 1–3). In the reactions of electron‐rich aziridines with C‐nucleophiles, SN2 reactions yielding anti‐type products were observed (Table 4). Reductive ring‐opening reaction by catalytic hydrogenation of (+)‐trans‐(2S,3R)‐3‐(1,3‐benzodioxol‐5‐yl)aziridine‐2‐carboxylate (+)‐trans‐ 3c afforded the corresponding α‐amino acid derivative, which was smoothly transformed into (+)‐tert‐butyl [(1R)‐2‐(1,3‐benzodioxol‐5‐yl)‐1‐methylethyl]carbamate((+)‐ 14 ) with high retention of optical purity (Scheme 6). 相似文献
Imidazolium salts (NHCewg ? HCl) with electronically variable substituents in the 4,5‐position (H,H or Cl,Cl or H,NO2 or CN,CN) and sterically variable substituents in the 1,3‐position (Me,Me or Et,Et or iPr,iPr or Me,iPr) were synthesized and converted into the respective [AgI(NHC)ewg] complexes. The reactions of [(NHC)RuCl2(CHPh)(py)2] with the [AgI(NHCewg)] complexes provide the respective [(NHC)(NHCewg)RuCl2(CHPh)] complexes in excellent yields. The catalytic activity of such complexes in ring‐closing metathesis (RCM) reactions leading to tetrasubstituted olefins was studied. To obtain quantitative substrate conversion, catalyst loadings of 0.2–0.5 mol % at 80 °C in toluene are sufficient. The complex with the best catalytic activity in such RCM reactions and the fastest initiation rate has an NHCewg group with 1,3‐Me,iPr and 4,5‐Cl,Cl substituents and can be synthesized in 95 % isolated yield from the ruthenium precursor. To learn which one of the two NHC ligands acts as the leaving group in olefin metathesis reactions two complexes, [(FL‐NHC)(NHCewg)RuCl2(CHPh)] and [(FL‐NHCewg)(NHC)RuCl2(CHPh)], with a dansyl fluorophore (FL)‐tagged electron‐rich NHC ligand (FL‐NHC) and an electron‐deficient NHC ligand (FL‐NHCewg) were prepared. The fluorescence of the dansyl fluorophore is quenched as long as it is in close vicinity to ruthenium, but increases strongly upon dissociation of the respective fluorophore‐tagged ligand. In this manner, it was shown for ring‐opening metathesis ploymerization (ROMP) reactions at room temperature that the NHCewg ligand normally acts as the leaving group, whereas the other NHC ligand remains ligated to ruthenium. 相似文献
Three aluminium complexes supported by a tetradentate pyrrolide ligand H2L [H2L = N,N′‐(2,2‐dimethylpropane‐1,3‐diyl)bis(1‐(1H‐pyrrol‐2‐yl)methanimine)], namely, Al(L)Me ( 1 ), Al(L)Cl ( 2 ), and Al(L)(OiPr) ( 3 ), were synthesized. The structures of 1 and 2 were established by X‐ray single crystal diffraction analysis, and the structure of 3 was characterized by NMR spectroscopy and element analysis. All complexes, containing different chemical bond forms (Al–C, Al–Cl, and Al–O), are good initiators for the ring‐opening polymerization (ROP) of ε‐caprolactone. The obtained polymers have high molecular weights (MWs) and relatively narrow molecular weight distributions (PDIs). Complexes 1 and 3 show dramatically high activities for the ROP of ε‐caprolactone. For complex 1 , when the monomer/initiator (M/I) ratio is 6400:1, a 40 % yield of the product could be obtained at 100 °C. The activity of 3 is higher than that of 1 , and 39 % yield of the polymers could be afforded at 70 °C, as the M/I value reaches 12800:1. The good activities of these complexes reveal their potential applications in industry. 相似文献
Reactions of the Grubbs 3rd generation complexes [RuCl2(NHC)(Ind)(Py)] (N‐heterocyclic carbene (NHC)=1,3‐bis(2,4,6‐trimethylphenylimidazolin)‐2‐ylidene (SIMes), 1,3‐bis(2,6‐diisopropylphenylimidazolin)‐2‐ylidene (SIPr), or 1,3‐bis(2,6‐diisopropylphenylimidazol)‐2‐ylidene (IPr); Ind=3‐phenylindenylid‐1‐ene, Py=pyridine) with 2‐ethenyl‐N‐alkylaniline (alkyl=Me, Et) result in the formation of the new N‐Grubbs–Hoveyda‐type complexes 5 (NHC=SIMes, alkyl=Me), 6 (SIMes, Et), 7 (IPr, Me), 8 (SIPr, Me), and 9 (SIPr, Et) with N‐chelating benzylidene ligands in yields of 50–75 %. Compared to their respective, conventional, O‐Grubbs–Hoveyda complexes, the new complexes are characterized by fast catalyst activation, which translates into fast and efficient ring‐closing metathesis (RCM) reactivity. Catalyst loadings of 15–150 ppm (0.0015–0.015 mol %) are sufficient for the conversion of a wide range of diolefinic substrates into the respective RCM products after 15 min at 50 °C in toluene; compounds 8 and 9 are the most catalytically active complexes. The use of complex 8 in RCM reactions enables the formation of N‐protected 2,5‐dihydropyrroles with turnover numbers (TONs) of up to 58 000 and turnover frequencies (TOFs) of up to 232 000 h?1; the use of the N‐protected 1,2,3,6‐tetrahydropyridines proceeds with TONs of up to 37 000 and TOFs of up to 147 000 h?1; and the use of the N‐protected 2,3,6,7‐tetrahydroazepines proceeds with TONs of up to 19 000 and TOFs of up to 76 000 h?1, with yields for these reactions ranging from 83–92 %. 相似文献
A magnesium‐catalyzed asymmetric ring‐opening reaction of aziridine with indole has been realized by employing commercially available chiral ligands. Both of the enantiomers of the ring‐opening product could be obtained with good yields and a high level of enantioselectivity. The corresponding ring‐opening product could be further transformed to various types of enantioenriched C3‐halogenated‐pyrroloindolines. 相似文献
Geminal dimethyl substituted N-acylaziridines react with diphenylacetonitrite (as anion), the course of the reaction depending on the nature of the acyl group. N-carbethoxy-2.2-dimethylaziridine undergoes abnormal aziridine ring opening at the gem.-substituted C atom and migration of the carbethoxy group accompanied by 5-membered ring closure to yield as major product N-2-carbethoxylamino-3.3-diphenyl-4.4-dimethylpyrroline-1 (1). In contrast, N-tosyl-2.2-dimethylaziridine undergoes normal ring opening at the less substituted C-atom with retention of the tosyl group on the original N-atom to form N-1-tosyl-2-imino-3.3-diphenyl-5.5-dimethylpyrrolidine (10). Deacylation of the N-carbethoxy- and N-tosyl derivatives yields the substituted 2-aminopyrrolines3, 9 and11. 相似文献
Polymers bearing activated aziridine groups are attractive precursors to α‐substituted‐β‐amino‐functionalized materials due to the enhanced reactivity of the pendant aziridine functionalities toward ring‐opening by nucleophiles. Two aziridine‐containing styrenic monomers, 2‐(4‐vinylphenyl)aziridine (VPA) and N‐mesyl‐2‐(4‐vinylphenyl)aziridine (NMVPA), were polymerized under a variety of reversible deactivation radical polymerization conditions. Low‐catalyst‐concentration atom transfer radical polymerization (LCC‐ATRP) and reversible addition‐fragmentation chain‐transfer (RAFT) polymerization were ineffective at producing well‐defined polymers from VPA due to side reactions between the aziridine functionalities and the agents controlling the polymerizations (catalysts or chain transfer agents). PolyVPA produced under nitroxide‐mediated polymerization (NMP) conditions had narrow molecular weight distribution at low to moderate conversions of monomer, but branched and eventually cross‐linked polymers were formed at higher conversions due to ring‐opening reactions of the aziridine groups. Most of these undesirable side reactions were eliminated by attaching a methanesulfonyl (mesyl) group to the aziridine nitrogen atom, and well‐defined linear homopolymers with targeted molecular weights were realized from NMVPA under RAFT and NMP conditions; however, side reactions between the aziridine groups and the catalyst in LCC‐ATRP still occured and the polymerization was uncontrolled using this technique.