共查询到20条相似文献,搜索用时 93 毫秒
1.
An investigation of the conversion of Δ1-3,4-cis-THC 1a to Δ6-3,4-trans-THC 2a with BBr3 is described. By use of 1a of known optical purity it was determined that the main epimerization occurs at C-4. The small loss of optical purity observed during formation of 2a results from either competitive epimerization at C-3 or a racemization process. The conversion of 3,4-cis- to 3,4-trans-HHCs proceeds with exclusive C-4 inversion. 相似文献
2.
《中国化学快报》2022,33(9):4253-4256
Two pairs of fluorescent natural products, talarolactones (+)/(?)-A and (+)/(?)-C [(+)/(?)-1 and (+)/(?)-2], were discovered and characterized as a new family of circularly polarized luminescence-active small organic molecules (CPL-SOMs) with high fluorescence efficiency and fascinating CPL properties. The CPL (|glum|) levels of enantiomerically pure (+)/(?)-1 and (+)/(?)-2 in solution falls into the usual range (10?5?10?3) considering their pure organic nature, but the sign of CPL were found to be closely related to the absolute configuration of C-8. The high agreement of the measured CPL spectra of (+)/(?)-1 and (+)/(?)-2 with the time-dependent density functional theory (TDDFT) calculated ones demonstrated the usefulness of CPL-calculation as a unique method for stereochemical assignment. This study may open up a new perspective for the stereochemical studies and the future development of CPL materials. 相似文献
3.
《Tetrahedron: Asymmetry》1999,10(2):297-306
A formal synthesis of (+)-vincamine (1) from (S)-(+)-2-ethyl-2-(2-methoxycarbonylethyl) cyclopentanone (6a) is described. This intermediate had previously been obtained by our research group in 90% ee through d'Angelo's deracemizing alkylation of the chiral imine 7, easily prepared from (R)-(+)-α-methylbenzylamine and 2-ethyl cyclopentanone with methyl acrylate. A potencial advanced intermediate for the synthesis of (+)-4, an epimer of (+)-1 at positions C-3 and C-14, has also been prepared from 6a. 相似文献
4.
Tsun-Hung Hsiao Tzu-Liang Wu Sandipan Chatterjee Chin-Yi Chiu Hon Man Lee Lorenzo Bettucci Claudio Bianchini Werner Oberhauser 《Journal of organometallic chemistry》2009,694(25):4014-4024
The imidazolium salts 1,1′-dibenzyl-3,3′-propylenediimidazolium dichloride and 1,1′-bis(1-naphthalenemethyl)-3,3′-propylenediimidazolium dichloride have been synthesized and transformed into the corresponding bis(NHC) ligands 1,1′-dibenzyl-3,3′-propylenediimidazol-2-ylidene (L1) and 1,1′-bis(1-naphthalenemethyl)-3,3′-propylenediimidazol-2-ylidene (L2) that have been employed to stabilize the PdII complexes PdCl2(κ2-C,C-L1) (2a) and PdCl2(κ2-C,C-L2) (2b). Both latter complexes together with their known homologous counterparts PdCl2(κ2-C,C-L3) (1a) (L3 = 1,1′-dibenzyl-3,3′-ethylenediimidazol-2-ylidene) and PdCl2(κ2-C,C-L4) (1b) (L4 = 1,1′-bis(1-naphthalenemethyl)-3,3′-ethylenediimidazol-2-ylidene) have been straightforwardly converted into the corresponding palladium acetate compounds Pd(κ1-O-OAc)2(κ2-C,C-L3) (3a) (OAc = acetate), Pd(κ1-O-OAc)2(κ2-C,C-L4) (3b), Pd(κ1-O-OAc)2(κ2-C,C-L1) (4a), and Pd(κ1-O-OAc)2(κ2-C,C-L2) (4b). In addition, the phosphanyl-NHC-modified palladium acetate complex Pd(κ1-O-OAc)2 (κ2-P,C-L5) (6) (L5 = 1-((2-diphenylphosphanyl)methylphenyl)-3-methyl-imidazol-2-ylidene) has been synthesized from corresponding palladium iodide complex PdI2(κ2-P,C-L5) (5). The reaction of the former complex with p-toluenesulfonic acid (p-TsOH) gave the corresponding bis-tosylate complex Pd(OTs)2(κ2-P,C-L5) (7). All new complexes have been characterized by multinuclear NMR spectroscopy and elemental analyses. In addition the solid-state structures of 1b·DMF, 2b·2DMF, 3a, 3b·DMF, 4a, 4b, and 6·CHCl3·2H2O have been determined by single crystal X-ray structure analyses. The palladium acetate complexes 3a/b, 4a/b, and 6 have been employed to catalyze the oxidative homocoupling reaction of terminal alkynes in acetonitrile chemoselectively yielding the corresponding 1,4-di-substituted 1,3-diyne in the presence of p-benzoquinone (BQ). The highest catalytic activity in the presence of BQ has been obtained with 6, while within the series of palladium-bis(NHC) complexes, 4b, featured with a n-propylene-bridge and the bulky N-1-naphthalenemethyl substituents, revealed as the most active compound. Hence, this latter precursor has been employed for analogous coupling reaction carried out in the presence of air pressure instead of BQ, yielding lower substrate conversion when compared to reaction performed in the presence of BQ. The important role of the ancillary ligand acetate in the course of the catalytic coupling reaction has been proved by variable-temperature NMR studies carried out with 6 and 7′ under catalytic reaction conditions. 相似文献
5.
《Tetrahedron: Asymmetry》1998,9(3):483-501
Alkyl halides behave differently to benzyl halides in C-1 alkylation of the title compounds. The syn and anti 1,4-disubstituted diastereomers thus obtained show different regioselectivity by further alkylation leading to the 1,4,4- and 1,1,4-trisubstituted compounds, respectively. Alkylation is always directed anti with respect to the bulkier substituent at C-1 or C-4. Debenzylation attempts on 2-benzyl-derivatives 1b by treatment with HCOOH and C/Pd or H2/C–Pd/MeOH/H+ led to C-1 oxidised or 7,8,9,10-tetrahydro-derivatives. Deprotection of 2-p-methoxybenzyl- and 2-(2,4-dimethoxybenzyl)-derivatives with CAN and with TFA/anisole, respectively, was successful, but in the latter case epimerization at C-1 occurred. 相似文献
6.
The biotransformation of botrydienediol (6) labelled with deuterium on carbons C-10 and C-15 has been studied. This has led to modification of some previous assumptions about the biodegradative route of botrydial. The [10-2H,15-2H]-botry-1(9)-4-diendiol (12) was transformed into dehydrobotrydienediol derivatives 13-15 but it was not incorporated into secobotryane skeleton (7). In addition, three new sesquiterpenoids have been isolated, which shed further light on the secondary metabolites of Botrytis cinerea. From the point of view of persistence of these toxins in the food chain, the easy biotransformation and different biodegradative routes of botrydial (1), seem to indicate that the toxin may not persist in the plant for a long time as it will be metabolized by the fungi and the plant. 相似文献
7.
Pei Tang Qi-Feng Chen Ling Wang Qiao-Hong Chen Xi-Xian Jian Feng-Peng Wang 《Tetrahedron》2012,68(27-28):5668-5676
O-Demethylation at C-1 in the C19-diterpenoid alkaloids is very challenging. In this paper, it was firstly observed that 10-OH group in deltaline (1) is a determining factor for the O-demethylation reaction. After removal of this hydroxyl group, 1-O-methyl group in the corresponding deltaline analogs can be readily removed by treatment with HBr–HOAc. Meanwhile, the C-14 atom in bromides 18 or 20 can be extruded under basic condition probably via a sequence, including Grob fragmentation, aerobic oxidation, deformylation, and SN2 nucleophilic substitution, to give enone 21 (70%) and oxetane 22 (14%). The structure of compound 22 was confirmed by X-ray crystallographic analysis of its derivative 21. 相似文献
8.
The interaction of Me3Al with Me2Al(acac) results in the carbonyl alkylation of the chelating acetylacetonate ligand and formation of trinuclear complex [MeAl][C12H20O4][AlMe2]2 (1). The title compound has been characterised by 1H-and 27Al-NMR spectroscopy. The 1H-NMR spectra are consistent with the presence of two distinct isomers in an equimolar ratio: cis-1 and trans-1. Both isomers contain two methylated acac units bridged by three organoaluminium moieties: central five-coordinated methyl aluminium species and two terminal four-coordinated dimethylaluminium species. The structure of cis-1 has been confirmed by X-ray crystallography which revealed that the five-coordinated aluminium atom rises in almost ideal square pyramidal geometry. The role of the molar ratio of reactants is discussed. 相似文献
9.
An ion formed by loss of 56 mass units from the molecular ion is often seen in mass spectra of trimethylsilyl ethers of C19 and C21 steroids having a 3β-hydroxy-Δ5 structure and an oxo group at C-17 or C-20. The nature of this fragment was investigated by the use of perdeuteriotrimethylsilyl ether derivatives and of [4-14C], [3-18O], [4,4-2H2] and [2,2,4,4-2H] labelled derivatives of 3β-hydroxy-5-androsten-17-one and 3β-hydroxy-5-pregnen-20-one. Evidence is presented to show that the neutral fragment of mass 56 is composed of carbon atoms 1, 2 and 3, the oxygen at C-3 and four hydrogen atoms. During the fragmentation process, the trimethylsilyl group and one of the hydrogens at C-2 are transferred to the fragment that carries the charge. 相似文献
10.
《Tetrahedron》1986,42(12):3203-3214
Full assignments of the 1H-nmr chemical shifts of the ring A protons in gibberellin A20 methyl ester 13-acetate have been made on the basis of 1H-, 2H- and 13C-nmr data of various deuteriated derivatives. These assignments have been used to prove that catalytic deuteriogenation of GA5-16, 17- epoxide-13-acetate is a syn-addition from the less hindered β-face accompanied by allylic exchange at C-1 giving isotopic labels at the 1β-, 2β- and 3β- positions. The position and stereochemistry of isotopic labelling was confirmed by comparison with an authentic sample of [1β,2β,3β-2H3] GA20 methyl ester 13-acetate prepared by methods which introduce deuterium stereoselectively at C-1, C-2 and C-3. The preparation of [2α-2H]GA20 and [3α-2H]GA20 is described. 相似文献
11.
Coraline Egloff Rafael Gramage-Doria Matthieu Jouffroy Dominique Armspach Dominique Matt Loïc Toupet 《Comptes Rendus Chimie》2013,16(6):509-514
Two imidazole-coordinating groups have been successfully grafted onto the C-6A and C-6D positions of permethylated α- and β-cyclodextrin scaffolds. Both water-soluble ligands L1 and L2 turned out to behave as good chelators when reacted with K2PtCl4. In the resulting diamagnetic cis-chelate complexes, the metal cation is pending above the cavity entrance. Paramagnetic ruthenium(III) chelate complexes have also been successfully synthesised from L1 and L2. In these more sterically demanding octahedral complexes, the imidazole groups coordinate the metal centre in a trans-fashion. 相似文献
12.
Wolfram Palitzsch Silke Nitsche Wilhelm Seichter Edwin Weber Gerhard Roewer 《Silicon Chemistry》2003,2(1-2):37-44
The reactions of substituted dichlorosilane monomers,Cl2SiRR′, with two equivalents of lithium aryl acetylide(1), LiC ≡ C-4-C6H4-Ph, afford RR′Si(C ≡ C-4-C6H4-Ph)2 (6: R,R′ =CH3; 7: R = CH3, R′ = CH=CH2; 8: R,R′ = Ph). An isomeric mixture of meso, (R,R)- and (S,S)-Bis[2-(N,N-dimethylaminomethyl)ferrocenyl]dichlorosilane (5) was used as starting chlorosilyl compound for reaction with LiC ≡ C-4-C6H4-Ph to give (FcN)2Si(C ≡ C-4-C6H4-Ph)2 (9). A detailedcharacterization of 6, 7, 8 and 9 has been carried out by 1H-NMR, 13C-NMR, 29Si-NMR, IR and UV-VIS spectroscopy. The crystal structure of 9 has been determined by X-ray diffraction analysis. 相似文献
13.
The uncatalyzed reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-quinones bearing either an electron withdrawing acetyl or a carbomethoxy group at C-2, was investigated. No reaction was observed using 1,4-quinones 8 and 9 bearing an ester group at C-2 whereas use of 1,4-quinones 10 and 11 bearing an acetyl group at C-2 only provided low yields of the silyloxythiophenes 15 and 16 resulting from electrophilic substitution of the silyloxythiophene by the 1,4-quinone. Use of the Lewis acids InCl3, Cu(OTf)2 and BF3·Et2O were investigated in an effort to improve the yield of the desired annulation reaction. BF3·Et2O proved to be the optimum catalyst for the synthesis of thiolactone naphthofuran adducts 14 and 18 from 1,4-naphthoquinones 9 and 11, respectively. Reaction of 2-tert-butyldimethylsilyloxythiophene 2 with 1,4-benzoquinones 8 and 10 bearing a carbomethoxy or an acetyl group at C-2, respectively, afforded thiolactone benzofuran adducts 13 and 17, respectively, catalyzed by either InCl3 or Cu(OTf)2. Addition of 2-tert-butyldimethylsilyloxythiophene 2 to 3-acetyl-5-methoxy-1,4-naphthoquinone 12 afforded adduct 19 that underwent oxidative rearrangement to thiolactone pyranonaphthoquinone 20 using ceric ammonium nitrate in acetonitrile, thus providing a novel approach for the synthesis of a thia analogue of the pyranonaphthoquinone antibiotic kalafungin. 相似文献
14.
Wanli Nie Wenqing Xu Maxim V. Borzov Dmitrii P. Krut’ko Judith A.K. Howard 《Journal of organometallic chemistry》2008,693(13):2355-2368
The novel bidentate ligand, C5H4CPh2CH2-(1-Me-C3H4N2) (3), has been prepared and characterized as its lithium salt LiC5H4CPh2CH2-(1-Me-C3H4N2) (3-Li). Cyclopentadiene HC5H4CPh2CH2-(1-Me-C3H4N2) (3-H) has been obtained from 6,6-diphenylfulvene and 1,2-dimethylimidazoline (1). In THF-d8 solution in the presence of 1, (1-methylimidazoline-2-yl)methyllithium (2) has been proved to undergo gradual conversion into a dilithium derivative of N1-methyl-N2-[(1E,2E)-1-methyl-2-(1-methylimidazolidine-2-idene)ethylidene]ethane-1,2-diamine (2a). In a solution, cyclopentadiene 3-H has been shown to undergo isomerization into 3-{N-[2-(N-methylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (4) and, further, into a mixture of 4 and two rotameric 3-[N-(2-aminoethyl)-N-methylamino]-1,1-diphenyl-1,2-dihydropentalenes (5a) and (5b). Treatment of the lithium salt 3-Li with Me3SiCl has lead to 3-{N-[2-(N-trimethylsilylamino)ethyl]amino}-1,1-diphenyl-1,2-dihydropentalene (6) as the dominant component in the reaction mixture. In the latter case the expected Me3Si-C5H4CPh2CH2-(1-Me-C3H4N2) (3-Si) was not observed. Stannylation of 3-Li with 1 equiv. of Me3SnCl has resulted in formation of a mixture of Me3Sn-C5H4CPh2CH2-(1-Me-C3H4N2) (3-Sn), (Me3Sn)2-C5H3CPh2CH2-(1-Me-C3H4N2) (3-Sn2), and cyclopentadiene 3-H in a ca. 2:1:1 molar ratio. Monocyclopentadienyl complexes {[η5:η1-κN-C5H4CPh2CH2-(1-Me-C3H4N2)]MCl3 (M = Ti (7), Zr (8)) have been prepared starting from the organotin and organolithium compounds 3-Sn and 3-Li, respectively. The dynamic behavior of complexes 7 and 8 has been investigated by means of variable-temperature NMR spectroscopy in solutions. The molecular structures of the dihydropentalene 4, binuclear complex {[η5:η1-κN-C5H4CPh2CH2-(1-Me-C3H4N2)]ZrCl2}2(μ-Cl)28, and a coordination dimer of the dilithium salt 2a have been established by X-ray diffraction analysis. In the crystal structure of the 2a-dimer, the shortest known Li-Li contact has been found. 相似文献
15.
Someshwar D. Dindulkar Paramasivam Parthiban Vedavati G. Puranik Yeon Tae Jeong 《Journal of Molecular Structure》2012
A series of N-benzylated 3,5-diakyl-2,6-diarylpiperidin-4-ones 4–8 were conveniently synthesized in significant yields of 68–88% by N-benzylation of the corresponding 2,6-diaryl-3,5-dimethylpiperidin-4-ones 1–3 using different benzyl bromides. Initially, the new piperidone 2,6-bis(4-ethoxyphenyl)-3,5-dimethylpiperidin-4-one 3 was synthesized by the condensation of 1:1:2 M ratio of 3-pentanone, ammonium acetate and para-ethoxybenzaldehyde in ethanolic medium. All the synthesized new compounds 3–8 were characterized by their analytical and spectral (IR, 1H and 13C NMR) interpretations. The stereochemistry of the new piperidone 3 was elucidated as chair conformation with an equatorial orientation of all substituents, suggested by its vicinal couplings from 1H NMR spectrum. To investigate the impact on piperidone stereochemistry as well as NMR chemical shifts, all the N-benzylated products 4–8 were compared with their corresponding precursors, and as a result, it is clearly established that all the synthesized N-benzyl piperidones exist in the chair conformation with an equatorial orientation of all the substituents at C-2, C-3, C-5, C-6 and N. Contrary to the probability all N-benzylated compounds retain the same conformation and configuration as their precursors, however, a remarkable change on the chemical shifts are observed. For the further unambiguous confirmation of stereochemistry, the 1-benzyl-3,5-dimethyl-2,6-diphenylpiperidin-4-one 4 was examined by single-crystal X-ray diffraction. The compound 4, C26H27NO, crystallized in a P-1 space group under triclinic system with unit cell dimensions a, b, c (Å) and α, β, γ (°) of 10.156(2), 11.002(2), 11.348(4) and 116.74(4), 100.81(3), 100.17(3), respectively. 相似文献
16.
Udai P. Singh Preeti Babbar Pooja Tyagi Thomas Weyhermüller 《Transition Metal Chemistry》2008,33(8):931-940
A novel Co(II) hydroxo complex Co{HB(3-tBu-5-iPrpz)3}(OH) 4 {where HB(3-tBu-5-iPrpz)3 = hydrotris(3-tert-butyl-5-isopropylpyrazol-l-yl)borate} has been prepared and its molecular structure has been determined by X-ray crystallography.
This complex is mononuclear with distorted tetrahedral geometry. The reaction of CO2 with Co{HB(3-tBu-5-iPrpz)3}(OH) resulted in the formation of a μ-carbonato bridged binuclear complex [Co{HB(3-tBu-5-iPrpz)3}]2(CO3) wherein the carbonate group is bound to both metal centers in an asymmetrical manner. In order to explore the role of labile
metal complexes in promoting ester hydrolysis, complexes [Co{HB(3,5-iPr2pz)3}]2(OH)2 and Co{HB(3-tBu-5-iPrpz)3}(OH) have been used as catalysts in the hydrolysis of both carboxylate as well as phosphate esters. The product of 4-nitrophenylacetate
hydrolysis with Co{HB(3-tBu-5-iPrpz)3}(OH) was isolated as four coordinate Co{HB(3-tBu-5-iPrpz)3}(OC6H4-4-NO2) 6, whereas the reaction of 4-nitrophenyltrifluoroacetate with [Co{HB(3,5-iPr2pz)3}]2(OH)2 resulted the formation of the six coordinate Co{HB(3,5-iPr2pz)3}(OC6H4-4-NO2)(MeCN)2 species.
Electronic supplementary material The online version of this article (doi:) contains supplementary material, which is available to authorized users.
相似文献
Udai P. SinghEmail: |
17.
Oseltamivir phosphate 1 was synthesized starting from a readily available acetonide, that is, ethyl (3R,4S,5R)-3,4-O-isopropylidene shikimate 2, through a new route via 11 steps and in 44% overall yield. The synthesis described in this article is characterized by two particular steps: the highly regioselective and stereoselective facile nucleophilic replacement of an OMs by an N3 group at the C-3 position of ethyl (3R,4S,5R)-3,4-O-bismethanesulfonyl-5-O-benzoyl shikimate 5, and the mild ring-opening of an aziridine with 3-pentanol at the C-1 position of ethyl (1S,5R,6S)-7-acetyl-5-benzoyloxy-7-azabicyclo[4,1,0]hept-2-ene-3-carboxylate 8. 相似文献
18.
《Tetrahedron: Asymmetry》2000,11(13):2765-2779
The ligands 6-[(diphenylphosphanyl)methoxy]-4,8-di-tert-butyl-2,10-dimethoxy-5,7-dioxa-6-phosphadibenzo[a,c]cycloheptene, 1, (S)-4-[(diphenylphosphanyl)methoxy]-3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4a′]dinaphthalene, (S)-2, and (S)-4-[(diphenylphosphanyl)methoxy]-2,6-bis-trimethylsilanyl-3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalene, (S)-3, (S)-2-(3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxymethyl)pyridine, (S)-4, and (S)-2-(3,5-dioxa-4-phosphacyclohepta[2,1-a;3,4-a′]dinaphthalen-4-yloxy)pyridine, (S)-5, have been easily prepared.The cationic complexes [Pd(η3-C3H5)(L-L′)]CF3SO3 (L–L′=1–(S)-5) and [Pd(η3-PhCHCHCHPh)(L–L′)]CF3SO3 (L–L′=(S)-2–(S)-4) were synthesized by conventional methods starting from the complexes [Pd(η3-C3H5)Cl]2 and [Pd(η3-PhCHCHCHPh)Cl]2, respectively. The behavior in solution of all the π-allyl- and π-phenylallyl-(L–L′)palladium derivatives 6–14 was studied by 1H, 31P{1H}, 13C{1H} NMR and 2D-NOESY spectroscopy. As concerns the ligands (S)-4 and (S)-5, a satisfactory analysis of the structures in solution was possible only for palladium–allyl complexes [Pd(η3-C3H5)((S)-4)]CF3SO3, 11, and [Pd(η3-C3H5)((S)-5)]CF3SO3, 12, since the corresponding species [Pd(η3-PhCHCHCHPh)((S)-4)]CF3SO3, 13, and [Pd(η3-PhCHCHCHPh)((S)-5)]CF3SO3, 14, revealed low stability in solution for a long time. The new ligands (S)-2–(S)-5 were tested in the palladium-catalyzed enantioselective substitution of (1,3-diphenyl-1,2-propenyl)acetate by dimethylmalonate. The precatalyst [Pd(η3-C3H5)((S)-2)]CF3SO3 afforded the allyl substituted product in good yield (95%) and acceptable enantioselectivities (71% e.e. in the S form). A similar result was achieved with the precatalyst [Pd(η3-C3H5)((S)-3)]CF3SO3. The nucleophilic attack of the malonate occurred preferentially at allylic carbon far from the binaphthalene moiety, namely trans to the phosphite group. When the complexes containing ligands (S)-4 and (S)-5 were used as precatalysts, the product was obtained as a racemic mixture in high yield. The number of the configurational isomers of the Pd-allyl intermediates present in solution in the allylic alkylation and the relative concentrations are considered a determining factor for the enantioselectivity of the process. 相似文献
19.
Sabrina Marie Martin Lutz Anthony L. Spek Robertus J.M. Klein Gebbink Gerard van Koten Nelly Kervarec Franois Michaud Jean-Yves Salaün Paul-Alain Jaffrs 《Journal of organometallic chemistry》2009,694(25):4001-4007
The O,O-diethyl thiophosphonate functional group has been introduced on position 2 of a pyrrole heterocycle following a two steps sequence that makes use of a [1,2] base-induced rearrangement applied for the first time to a O,O-diethyl thiophosphoramide intermediate. This rearrangement has been studied by low temperature NMR and the intermediates have been fully characterized. The coordination of this monoanionic bidentate (N,Ssp2) ligand to silver or palladium is studied The bidentate ligand 2 (O,O-diethyl pyrrol-2-ylthiophosphonate), associated with a palladium precursor, produces in the presence of triethylamine the complex trans-[Pd(η2-2′)2] 3 (2′ is deprotonated ligand 2). Ligand 2 also reacts with silver oxide in dichloromethane to give an unstable complex 2′-Ag that can be stabilized by addition of triphenylphosphine to produce the coordination complex 4 [Ag((η2-2′)(PPh3)2]. 相似文献
20.
Vladimir N. Belov Michael Brands Jochen Krüger Viktor Sokolov Armin de Meijere 《Tetrahedron》2004,60(35):7579-7589
Enantiomerically pure N2-Z-N2-MeAsnOH [(S)-14], prepared in 8 steps (23% overall yield) from asparaginic acid, was first subjected to a Hofmann degradation with PhI(OCOCF3)2 yielding (S)-N2-Z-N2-methyl-2,3-diaminopropanoic acid [N2-Z-N2-Me-L-A2pr, (S)-15], and this in turn was protected to give N2-Z-N3-Boc-N2-Me-L-A2pr [(S)-17]. Condensation of (S)-17 with HNC(SMe)NHCONH2 followed by removal of the tert-butoxycarbonyl protecting group, cyclization and hydrogenolytic removal of the Z-group gave the heterocycle of TAN-1057A [(S)-1] with an e.e. of 87 in 36% yield [from (S)-14]. Coupling of (S)-1 with (S)-tris-Z-β-homoarginine (20a) in the presence of O-(7-azabenzotriazol-1-yl)-N,N,N′,N′-tetramethyluronium hexafluorophosphate (HATU) and iPr2NEt in N,N-dimethylacetamide followed by hydrogenolysis afforded the most active A-diastereomer of the natural antibiotic TAN-1057 in 52% yield (from (S)-1 and 20a). Similarly, starting from (S)-1, a single diastereomer of the potent, less toxic TAN-1057A analogue 22b with a β-lysine side chain has been prepared. All described synthetic steps do not require column chromatography for purification of the products. 相似文献