首页 | 本学科首页   官方微博 | 高级检索  
相似文献
 共查询到20条相似文献,搜索用时 500 毫秒
1.
Treatment of N,N′‐bis(aryl)formamidines (FXylH = N,N′‐bis(2,6‐dimethylphenyl)formamidine, FEtH = N,N′‐bis(2,6‐diethylphenyl)formamidine, FisoH = N,N′‐bis(2,6‐diisopropylphenyl)formamidine) with nBuLi in the presence of tmeda (= N,N,N′,N′‐tetramethylethylenediamine) led to deprotonation of the amidine affording [Li(FXyl)(tmeda)] ( 1 ), [Li(FEt)(tmeda)] ( 2 ) and [Li(Fiso)(tmeda)] ( 3 ) respectively. Similar treatment of FXylH and FisoH with [Na{N(SiMe3)2}] in THF and pmdeta (= N,N,N′,N″,N″‐pentamethyldiethylenetriamine) yielded [Na(FXyl)(pmdeta)] ( 4 ) and [Na(Fiso)(pmdeta)] ( 5 ). All complexes were characterised by spectroscopy (NMR and IR) and X‐ray crystallography. Due to the bulkiness of the formamidinate ligands and the multidentate nature of the supporting neutral amine ligands (tmeda and pmdeta), all compounds were mononuclear with η2‐chelating formamidinate ligands in the solid state.  相似文献   

2.
Additions of beryllium–halide bonds in the simple beryllium dihalide adducts, [BeX2(tmeda)] (X=Br or I, tmeda=N,N,N′,N′‐tetramethylethylenediamine), across the metal center of a neutral aluminum(I) heterocycle, [:Al(DipNacnac)] (DipNacnac=[(DipNCMe)2CH]?, Dip=2,6‐diisopropylphenyl), have yielded the first examples of compounds with beryllium–aluminum bonds, [(DipNacnac)(X)Al‐Be(X)(tmeda)]. For sake of comparison, isostructural Mg–Al and Zn–Al analogues of these complexes, viz. [(DipNacnac)(X)Al‐M(X)(tmeda)] (M=Mg or Zn, X=I or Br) have been prepared and structurally characterized. DFT calculations reveal all compounds to have high s‐character metal–metal bonds, the polarity of which is consistent with the electronegativities of the metals involved. Preliminary reactivity studies of [(DipNacnac)(Br)Al‐Be(Br)(tmeda)] are reported.  相似文献   

3.
Voilà, optical activity : Both enantiomers of 1‐chloroindene have been synthesized in high selectivity from solely achiral starting materials, and without using optically active catalysts (see scheme). These symmetry‐breaking syntheses provide a proof‐of‐concept for a new approach to asymmetric synthesis. NCS=N‐chlorosuccinimide.

  相似文献   


4.
On the 1H NMR timescale, 2,2′‐biindolyls with (R)‐configured (1‐alkoxyprop)‐2‐yl, (1‐hydroxyprop)‐2‐yl, or (1‐siloxyprop)‐2‐yl substituents at C‐1 and C‐1′ are atropisomerically stable at <0 °C and interconvert at >30 °C. A 2,2′‐biindolyl (R,R)‐ 17 a of that kind and achiral (!) brominating reagents gave the atropisomerically stable 3,3′‐dibromobiindolyls (M)‐ and/or (P)‐ 18 a at best atropselectively—because of point‐to‐axial asymmetric inductions—and atropdivergently, exhibiting up to 95 % (M)‐ and as much (P)‐atropselectivity. This route to atropisomerically pure biaryls is novel and should extend to other substrates and/or different functionalizations. The dibromobiindolyls (M)‐ and (P)‐ 18 a furnished the biindolyldiphosphanes (M)‐ and (P)‐ 14 without atropisomerization. These syntheses did not require the resolution of a racemic mixture, which distinguishes them from virtually all biaryldiphosphane syntheses known to date. (M)‐ and (P)‐ 14 acted as ligands in catalytic asymmetric allylations and hydrogenations. Remarkably, the β‐ketoester rac‐ 25 c was hydrogenated trans‐selectively with 98 % ee; this included a dynamic kinetic resolution.  相似文献   

5.
The novel zwitterionic heterocycle 1 was unexpectedly obtained from the reaction between [Li(SiR3)(thf)3] and ArNC. Upon heating 1 underwent an interesting ring opening to give the alkyne 2 . Hence the C≡C bond effectively arises from the C−C coupling of two ArNC moieties. R=SiMe3, Ar=2,6‐Me2C6H3, tmeda=N,N,N′,N′‐tetramethylethylenediamine.  相似文献   

6.
A six‐step asymmetric total synthesis of (20S)‐camptothecin ( 1 ) has been accomplished in 25% overall yield starting from the known pyridone 3 . The key steps in this synthesis are the chemoselective Ni‐catalyzed hydrogenation of 3‐cyanopyridone 6 to 3‐formylpyridone 7 in AcOH/pyridine/H2O and the Davis asymmetric hydroxylation of tricyclic lactone 4 utilizing a chiral N‐sulfonyloxaziridine into (4′S)‐tricyclic hydroxylactone 2 .  相似文献   

7.
The reaction of (η5‐(N,N‐dimethylaminomethyl)cyclopentadien‐yl)(η4‐tetraphenylcyclobutadiene)cobalt with sodium tetrachloropalladate and (R)‐N‐acetylphenylalanine gave planar chiral palladacycle di‐μ‐chloridebis[(η5‐(Sp)‐2‐(N,N‐dimethylaminomethyl)cyclopentadienyl,1‐C,3′‐N)(η4‐tetraphenylcyclobutadiene)cobalt]dipalladium [(Sp)‐Me2‐CAP‐Cl] in 92 % ee and 64 % yield. Enantiopurity (>98 % ee) was achieved by purification of the monomeric (R)‐proline adducts and conversion back to the chloride dimer. Treatment with AgOAc gave (Sp)‐Me2‐CAP‐OAc which was applied to asymmetric transcyclopalladation (up to 78 % ee). The (R)‐N‐acetylphenylalanine mediated palladation methodology was applicable also to the corresponding N,N‐diethyl (82 % ee, 39 % yield) and pyrrolidinyl (>98 % ee, 43 % yield) cobalt sandwich complexes. A combination of 5 mol % of the latter [(Sp)‐Pyrr‐CAP‐Cl] and AgNO3 (3.8 equiv) is a catalyst for the allylic imidate rearrangement of an (E)‐N‐aryltrifluoroacetimidate (up to 83 % ee), and this catalyst system is also applicable to the rearrangement of a range of (E)‐trichloroacetimidates (up to 99 % ee). This asymmetric efficiency combined with the simplicity of catalyst synthesis provides accessible solutions to the generation of non‐racemic allylic amine derivatives.  相似文献   

8.
Treatment of (aR)‐[1,1′binaphthalene]‐8,8′‐diol ((−)‐ 1 ) with hexamethylphosphorous triamide afforded the N,N‐dimethylphosphoramidite (−)‐ 3 (Scheme 1). The synthesis of the analogous N,N‐diisopropylphosphoramidite 4 failed, however, and afforded the acyclic phosphonamidate (−)‐ 5 . The application of the cyclic phosphoramidite (−)‐ 3 towards asymmetric catalysis was investigated. The borane reduction of acetophenone ( 6 ) to (R)‐1‐phenylethanol ( 7 ) in the presence of (−)‐ 3 proceeded with 96% ee (Scheme 2). The use of (−)‐ 3 as ligand in several Cu‐catalyzed addition and substitution reactions resulted in enantioselectivities ranging from 0 to 50% (Schemes 3 and 4).  相似文献   

9.
Enantiomerically pure tribenzotriquinacenes (TBTQs) bearing two monofunctionalized aromatic nuclei were synthesized for the first time and their optical properties and absolute configuration determined. A remarkably regioselective bis‐formylation of the fully bridgehead methylated parent TBTQ hydrocarbon with MeOCHCl2/TiCl4 afforded a mixture of two Cs‐symmetrical (achiral) difunctionalized derivatives together with one C1‐symmetrical (chiral) isomer. Reduction and subsequent column chromatography furnished the three respective benzylic TBTQ dialcohols. Optical resolution of the racemic 2,6‐bis(hydroxymethyl) derivative was achieved via the diastereomeric (R)‐1,1′‐bi‐2‐naphthol ethers and the absolute configuration of the enantiomers was determined by CD exciton model analysis. The electronic circular dichroism (ECD) spectra and the specific rotation of the enantiomers were found to agree with the results of DFT calculations. Among the Cs‐symmetrical isomers, the “proximal” 2,11‐dialdehyde and the corresponding benzylic dialcohol were identified by 2D NMR spectroscopy and X‐ray crystallographic analysis, respectively, and used as the starting point for the synthesis of several novel dithiametacyclophanes. These include the first “dimeric” tribenzotriquinacene‐based cyclophanes bearing the bowls of the two TBTQ units attached to each other in a syn (concave–concave) or anti (convex–concave) configuration. The usefulness of such thiacyclophanes as fluorescent chemosensors for different metal ions is also demonstrated.  相似文献   

10.
Allylation, trans‐ and cis‐crotylation of (2E,4E)‐2,4‐dimethylhexadienal, a representative α,β,γ,δ‐unsaturated aldehyde, was carried out under different catalytic and stoichiometric conditions. The reactions catalyzed by organocatalysts TRIP‐PA and N,N′‐dioxides gave the best results with respect to yields, asymmetric induction, and catalyst load in comparison to other procedures. The developed methodology was applied in the enantioselective synthesis of (5R,6S)‐(+)‐pteroenone, a defensive metabolite (ichthyodeterrent) of the Antarctic pteropod Clione antarctica.  相似文献   

11.
A series of new octahydro‐1,1′‐binaphthyl derivatives, namely (R)‐(+)‐2‐(N, N‐dialkylamino)‐2′‐hydroxy‐5,5′,6,6′,7, 7′,8,8′‐octahydro‐1,1′‐binaphthyls (7,9), have been synthesized. Their asymmetric induction for enantioselective addition of Et2Zn to benzaldehyde was examined and it was found that (R)‐(+)‐2‐(N‐cyclohexyl‐N‐methylamino)‐2′‐hydroxy‐5, 5′,6,6′,7,7′,8,8′‐octahydro‐1,1′‐binaphthyl (9c) exhibited the best asymmetric induction among the ligands prepared, up to 55% ee of 1‐phenylpropanol being obtained.  相似文献   

12.
Chiral secondary alkylcopper reagents were prepared from chiral secondary alkyl iodides by a retentive I/Li exchange followed by a retentive transmetalation with CuBr?P(OEt)3. Switching the solvent to THF significantly increased their configurational stability and made these copper reagents suitable for regioselective allylic substitutions. The optically enriched copper species underwent SN2 substitutions with allylic bromides (up to >99 % SN2 regioselectivity). The addition of ZnCl2 and the use of chiral allylic phosphates allowed to switch the regioselectivity towards SN2′ substitution (up to >99 % SN2′ regioselectivity) and to perform highly selective anti‐SN2′ substitutions with absolute control over two adjacent stereocenters. This method was applied in the total synthesis of the three ant pheromones (+)‐lasiol, (+)‐13‐norfaranal, and (+)‐faranal (up to 98:2 dr, 99 % ee).  相似文献   

13.
The 3‐methyl‐4‐(tricyclo[5.2.1.02,6]dec‐4‐en‐8‐ylidene)butan‐2‐ols (=Fleursandol®; rac‐ 10 ), a new class of sandalwood odorants, were synthesized in their enantiomerically pure forms by use of tricyclo[5.2.1.02,6]dec‐4‐en‐8‐ones 17 and ent‐ 17 and (tetrahydro‐2H‐pyran‐2‐yl)‐protected 4‐bromo‐3‐methylbutan‐2‐ols 22 and ent‐ 22 as starting materials (Schemes 2–4). Only four of 16 possible stereoisomers of rac‐ 10 possess the typical, very pleasant, long‐lasting sandalwood odor (Table 1). The (2S,3R,4E,1′R,2′R,6′R,7′R)‐isomer ent‐ 10a is by far the most important representative, with an odor threshold of 5 μg/l in H2O.  相似文献   

14.
A highly efficient Ru catalyst based on an achiral, very simple, and inexpensive amino alcohol ligand (2‐amino‐2‐methylpropan‐1‐ol) has been developed for the asymmetric transfer hydrogenation (ATH) of chiral N‐(tert‐butylsulfinyl)imines. This complex is able to catalyze the ATH of both aromatic and the most challenging aliphatic sulfinylimines by using isopropyl alcohol as the hydrogen source. The diastereoselective reduction of aromatic, heteroaromatic, and aliphatic sulfinylketimines, including sterically congested cases, over short reaction times (1–4 h), followed by desulfinylation of the nitrogen atom, affords the corresponding highly enantiomerically enriched (ee up to >99 %) α‐branched primary amines in excellent yields. The same ligand was equally effective for the synthesis of both (R)‐ and (S)‐amines by using the appropriate absolute configuration in the iminic substrate. DFT mechanistic studies show that the hydrogen‐transfer process is stepwise. Moreover, the origin of the diastereoselectivity has been rationalized.  相似文献   

15.
The Staudinger reaction of organic azides tBuN3, 1‐Ad‐N3, and DippN3 (Dipp = 2,6‐diisopropylphenyl) with (R)‐N,N′‐bis(diphenylphosphanyl)‐2,2′‐diamino‐1,1′‐binaphthyl [(R)‐Binam‐P], obtained by an optimized procedure from (R)‐(+)‐Binam, Ph2PCl, and Et3N in DCM, leads to preparation of a series of new C2‐symmetric bis‐iminophosphonamide ligands [(R)‐Binam(Ph2PN(H)R)2] [R = tBu ( 1 ), Ad ( 2 ), and Dipp ( 3 )]. The molecular structure of 1· 2DMSO was confirmed by X‐ray structure analysis.  相似文献   

16.
A highly efficient asymmetric cascade reaction between keto esters and alkynyl alcohols and amides is reported. The success of the reaction was attributed to the combination of chiral Lewis acid N,N′‐dioxide nickel(II) catalysis with achiral π‐acid gold(I) catalysis working as an asymmetric relay catalytic system. The corresponding spiroketals and spiroaminals were synthesized in up to 99 % yield, 19:1 d.r., and more than 99 % ee under mild reaction conditions. Control experiments suggest that the N,N′‐dioxide ligand was essential for the formation of the spiro products.  相似文献   

17.
The absolute configuration of decipinone ( 2 ), a myrsinane‐type diterpene ester previously isolated from Euphorbia decipiens, has been determined by NMR study of its axially chiral derivatives (aR)‐ and (aS)‐N‐hydroxy‐2′‐methoxy‐1,1′‐binaphthalene‐2‐carboximidoyl chloride ((aR)‐MBCC ( 3a ) and (aS)‐MBCC ( 3b )). The absolute configurations at C(7) and C(13) of 2 determined were (R) and (S), respectively. Therefore, considering the relative configuration of 2 , the absolute configuration determined was (2S,3S,4R,5R,6R,7R,11S,12R,13S,15R).  相似文献   

18.
A straightforward and scalable eight‐step synthesis of new N‐heterocyclic carbenes (NHCs) has been developed from inexpensive and readily available 2‐nitro‐m‐xylene. This process allows for the preparation of a novel class of NHCs coined ITent (“Tent” for “tentacular”) of which the well‐known IMes (N,N′‐bis(2,4,6‐trimethylphenyl)imidazol‐2‐ylidene), IPr (N,N′‐bis(2,6‐di(2‐propyl)phenyl)imidazol‐2‐ylidene) and IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene) NHCs are the simplest and already known congeners. The synthetic route was successfully used for the preparation of three members of the ITent family: IPent (N,N′‐bis(2,6‐di(3‐pentyl)phenyl)imidazol‐2‐ylidene), IHept (N,N′‐bis(2,6‐di(4‐heptyl)phenyl)imidazol‐2‐ylidene) and INon (N,N′‐bis(2,6‐di(5‐nonyl)phenyl)imidazol‐2‐ylidene). The electronic and steric properties of each NHC were studied through the preparation of both nickel and palladium complexes. Finally the effect of these new ITent ligands in Pd‐catalyzed Suzuki–Miyaura and Buchwald–Hartwig cross‐couplings was investigated.  相似文献   

19.
A concise asymmetric synthesis of the gastroprokinetic agent (+)-(3S,4R)-cisapride {(+)-(3S,4R)-N(1)-[3′-(4″-fluorophenoxy)propyl]-3-methoxy-4-(2″′-methoxy-4″′-amino-5″′-chlorobenzamido)piperidine} from commercially available starting materials has been developed. The key step of this synthesis employs the diastereoselective conjugate addition of lithium (R)-N-benzyl-N-(α-methylbenzyl)amide to tert-butyl 5-[N-3′-(4″-fluorophenoxy)propyl-N-allylamino]pent-2-enoate and in situ enolate oxidation with (?)-camphorsulfonyloxaziridine to set the (3S,4R)-configuration found within the piperidine ring of the product. This synthesis proceeds in 9 steps from commercially available 1-(4′-fluorophenoxy)-3-bromopropane with an overall yield of 19%.  相似文献   

20.
A new coordination polymer, catena‐poly[[(dipyrido[3,2‐a:2′,3′‐c]phenazine‐κ2N,N′)nickel(II)]‐μ‐2,6‐dipicolinato‐κ4O2,N,O6:O2′], [Ni(C7H3NO4)(C18H10N4)]n, exhibits a one‐dimensional structure in which 2,6‐dipicolinate acts as a bridging ligand interconnecting adjacent nickel(II) centers to form a chain structure. The asymmetric unit contains one NiII center, one dipyrido[3,2‐a:2′,3′‐c]phenazine ligand and one 2,6‐dipicolinate ligand. Each NiII center is six‐coordinated and surrounded by three N atoms and three O atoms from one dipyrido[3,2‐a:2′,3′‐c]phenazine ligand and two different 2,6‐dipicolinate ligands, leading to a distorted octahedral geometry. Adjacent chains are linked by π–π stacking interactions and weak interactions to form a three‐dimensional supramolecular network.  相似文献   

设为首页 | 免责声明 | 关于勤云 | 加入收藏

Copyright©北京勤云科技发展有限公司  京ICP备09084417号