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1.
Giuseppe Faita 《Tetrahedron》2010,66(16):3024-5854
The asymmetric Friedel-Crafts reaction between methyl (E)-2-oxo-4-aryl-3-butenoates (1a-c) and activated benzenes (2a-d) has been efficiently catalyzed by the ScIII triflate complex of (4′S,5′S)-2,6-bis[4′-(triisopropylsilyl) oxymethyl-5′-phenyl-1′,3′-oxazolin-2′-yl]pyridine (pybox 3). The 4,4-diaryl-2-oxo-butyric acid methyl esters (4) are usually formed in good yields and the enantioselectivity is up to 99% ee. The sense of the stereoinduction can be rationalized with the same octahedral complex (10) between 1, pybox 3 and Sc triflate already proposed for other reactions involving pyruvates, and catalyzed by the same complex. 相似文献
2.
Rui-Heng ZhuXiao-Xin Shi 《Tetrahedron: Asymmetry》2011,22(4):387-393
A novel and simple process for the preparation of enantiomerically pure (SS)-benzenesulfinamide (SS)-3a, (SS)-p-toluenesulfinamide (SS)-3b, (SS)-p-chloro-benzenesulfinamide (SS)-3c and (SS)-p-fluorobenzenesulfinamide (SS)-3d has been developed. The treatment of arylsulfinyl chlorides with (R)-N-benzyl-1-phenylethanamine in the presence of excess triethylamine gave diastereomeric mixtures of N-benzyl-N-(1-phenylethyl)-arylsulfinamides 1, which underwent spontaneous crystallization to furnish diastereomerically pure (R,SS)-N-benzyl-N-(1-phenylethyl)-arylsulfinamides (R,SS)-1a-1d in 28%, 29%, 27% and 31% yields, respectively. The diastereomerically pure compounds (R,SS)-1 were then converted into four enantiopure (RS)-methyl arylsulfinates (RS)-2, and finally into four enantiopure (SS)-arylsulfinamides (SS)-3 in good yields. 相似文献
3.
Maria Daoudi Abdelali Kerbal Jean-Pierre Launay Taibi Ben Hadda Pierre H. Dixneuf 《Tetrahedron》2006,62(13):3123-3127
A series of tridentate ligands N,N-bis-[(di-substituted-1-pyrazolyl)methyl]arylamines 2-3a,b and benzylamine 4a,b, tetradentate N,N′-bis-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 7a,b and hexadentate N,N,N′,N′-tetra-[(di-substituted-1-pyrazolyl)methyl]para-phenylenediamines 8a,b has been prepared in good yield by condensation of arylamines, benzylamine or para-phenylenediamine with N-hydroxymethyl disubstituted pyrazoles 1a,b. The synthesis and characterisation of these various polydentate ligands are described. 相似文献
4.
To synthesize (3′R,5′S)-3′-hydroxycotinine [(+)-1], the main metabolite of nicotine (2), cycloaddition of C-(3-pyridyl)nitrones 3a, 3c, and 15 with (2R)- and (2S)-N-(acryloyl)bornane-10,2-sultam [(2R)- and (2S)-8] was examined. Among them, l-gulose-derived nitrone 15 underwent stereoselective cycloaddition with (2S)-8 to afford cycloadduct 16, which was elaborated to (+)-1. 相似文献
5.
Jamie F BickleyStanley M Roberts Ye RunhuiJohn Skidmore Corina B Smith 《Tetrahedron》2003,59(30):5731-5736
Optically active (4S,5R)-dihydroisoxazoles 5a-c (90-91% ee) have been prepared by reaction of the epoxyketones 4a-c with hydroxylamine. Reduction of compounds 5a and 5b using lithium aluminium hydride took place exclusively from the Re face to give (1R,2S,3S)-1,3-disubstituted-3-aminopropane-1,2-diols 6a and 6b. These amino-diols were characterised by N-acetylation and the stereochemical sense of the hydride reduction was confirmed by conversion of amides 7a and 7b into α-amino acid derivatives 10a and 10b. 相似文献
6.
Grzegorz Mlostoń Dorota RygielskaMarcin Jasiński Heinz Heimgartner 《Tetrahedron: Asymmetry》2011,22(6):669-674
A new exploration of monoprotected derivatives of trans-1,2-diaminocyclohexane as a platform for the synthesis of enantiomerically pure imidazole derivatives is described. The primary amino group (-NH2), present in the mono-imine derivative of salicylic aldehyde (hemi-salen derivative) 5 was used for sequential reactions with formaldehyde and the corresponding α-(hydroxyimino)ketone. (S)-(−)-1-Phenylethylamine was also used as starting material for the preparation of new imidazole N-oxides 7c and 10a-c, bearing a chiral N-(1-phenylethyl)carboxamido function at C(4). Imidazole N-oxides 10a,b possessing either a Me or i-Pr group at N(1), respectively, follow the known sulfur-transfer pathway to afford the corresponding imidazole-2-thiones 13a,b. However, in the case of imidazole N-oxide 10c with a bulky adamantan-1-yl substituent at N(1), the attempted ‘sulfur-transfer reaction’ led to the deoxygenated imidazole derivative 14. Finally, the same reaction with 7c, which bears an electron-withdrawing N-(1-phenylethyl)carboxamide residue at C(4) of the imidazole ring, yielded a mixture of deoxygenated imidazole 16 and imidazole-2-thione 15c. 相似文献
7.
Lipase-catalyzed hydrolysis of (E)-2-[α-(acetoxyimino)benzyl]-1,1′-binaphthyl [(±)-1a] and (Z)-2-[α-(acetoxyimino)benzyl]-1,1′-binaphthyl [(±)-1b] yielded optically active (E)-2-[α-(hydroxyimino)benzyl]-1,1′-binaphthyl [(S)-2a] and (Z)-2-[α-(hydroxyimino)benzyl]-1,1′-binaphthyl [(R)-2b], respectively, with high enantiomeric excess. Selectivity for the opposite enantiomer of the axial binaphthyl skeleton was shown by (Z)-isomer 1b against (E)-isomer 1a. 相似文献
8.
Douglas Onyancha Vincent Nyamori Christopher Imrie Thomas I.A. Gerber 《Journal of organometallic chemistry》2009,694(2):207-1132
The efficient and simple routes for the synthesis of various ferrocenyl derivatives from ferrocenylcarbinols and N,N′-thiocarbonyldiimidazole (TCDI) are described. It involves grinding the two substrates in a Pyrex tube with a glass rod at room temperature. The reaction of ferrocenylmethanol (1a) provided S,S-bis(ferrocenylmethyl)dithiocarbonate (1b), whose crystal structure and a plausible mechanism for its formation are also reported. The reaction of 1-ferrocenyl-1-phenylmethanol (2a) and 1-ferrocenylbutanol (2b) gave the products 2c and 2d, respectively. The reaction of ω-ferrocenyl alcohols 4-ferrocenylphenol (3a) and 6-ferrocenylhexan-1-ol (3b) yielded the products 3c and 3d, respectively. Reaction of 1,1′-ferrocenedimethanol (3e) afforded 3f in moderate yield, and by contrast, it was not similar to 1b. Reaction of [4-(trifluoromethyl)phenyl]methanol (4a) provided the thiocarbonate 4b in good yield. 相似文献
9.
Robert W. Baker Simon O. Rea Elisabeth M.C. Schenkelaars Angela Totaro 《Tetrahedron》2005,61(15):3733-3743
Racemic 1-(1′-isoquinolinyl)-2-naphthalenemethanol rac-12 was prepared through a ligand coupling reaction of racemic 1-(tert-butylsulfinyl)isoquinoline rac-7 with the 1-naphthyl Grignard reagent 10. Resolution of rac-12 was achieved through chromatographic separation of the Noe-lactol derivatives 14 and 15, providing (R)-(−)-12 of >99% ee and (S)-(+)-12 of 90% ee. The ligand coupling reaction of optically enriched sulfoxide (S)-(−)-7 (62% ee) with Grignard reagent 10 furnished rac-12, with the absence of stereoinduction resulting from competing rapid racemisation of the sulfoxide 7. Reaction of optically enriched (S)-(−)-7 with 2-methoxy-1-naphthylmagnesium bromide was also accompanied by racemisation of the sulfoxide 7, and furnished optically active (+)-1-(2′-methoxy-1′-naphthyl)isoquinoline (+)-3b in low enantiomeric purity (14% ee). The absolute configuration of (+)-3b was assigned as R using circular dichroism spectroscopy, correcting an earlier assignment based on the Bijvoet method, but in the absence of heavy atoms. Optically active 2-pyridyl sulfoxides were found not to undergo racemisation analogous to the 1-isoquinolinyl sulfoxide 7, with the ligand coupling reactions of (R)-(+)- and (S)-(−)-2-[(4′-methylphenyl)sulfinyl]-3-methylpyridines, (R)-(+)-17 and (S)-(−)-17, with 2-methoxy-1-naphthylmagnesium bromide providing (−)- and (+)-2-(2′-methoxy-1′-naphthyl)-3-methylpyridines, (−)-18 and (+)-18, in 53 and 60% ee, respectively. The free energy barriers to internal rotation in 3b and 18 have been determined, and the isoquinoline (R)-(−)-12 examined as a ligand in the enantioselectively catalysed addition of diethylzinc to benzaldehyde; (R)-(−)-12 was also converted to (R)-(−)-N,N-dimethyl-1-(1′-isoquinolinyl)-2-naphthalenemethanamine (R)-(−)-19, and this examined as a ligand in the enantioselective Pd-catalysed allylic substitution of 1,3-diphenylprop-2-enyl acetate with dimethyl malonate. 相似文献
10.
Paulo H.G. Zarbin Alfredo R.M. de OliveiraCarlos E. Delay 《Tetrahedron letters》2003,44(36):6849-6851
A diastereoselective approach to (2R,5S)- and (2S,5S)-2-methyl-1,6-dioxaspiro[4.5]decane 1 and 1a is described. The route starts with an alkylation reaction among the cyclopentanone N,N-dimethylhydrazone 6 and the chiral iodides (R)-3 or (S)-3, derived from the enantiomers of ethyl β-hydroxybutyrate, controlling the estereocenter at C-2 of the molecules. The alkylated products 7 and 7a were easily transformed into the 1,8-O-TBS-1,8-dihydroxy-5-nonanones 9 and 9a in four steps, and a subsequent stereoselective spiroketalization, in acidic media, afforded a Z:E mixture (1:2) of compounds 1 and 1a. 相似文献
11.
Yong-Gang Wang 《Tetrahedron》2007,63(26):6042-6050
Chiral phase-transfer catalysts (S)-1a, (S)-1b, and (S)-2 with conformationally fixed biphenyl cores were conveniently prepared from the known, easily available (S)-6,6′-dimethylbiphenyl-2,2′-diol 3 and (S)-4,5,6,4′,5′,6′-hexamethoxybiphenyl-2,2′-dicarboxylic acid 14, respectively, in five steps. The catalysts, (S)-1a and (S)-1b are readily applicable to asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester with excellent enantioselectivity. In particular, catalyst (S)-1b was found to exhibit the unique temperature effect on the enantioselectivity, and asymmetric alkylation of glycine derivatives at room temperature gave higher enantiomeric excess than that at 0 °C. In addition, the catalyst (S)-2 exhibited the high catalytic performance (0.01-1 mol %) in the asymmetric alkylation of N-(diphenylmethylene)glycine tert-butyl ester and N-(p-chlorophenylmethylene)alanine tert-butyl ester compared to the existing chiral phase-transfer catalysts, thereby allowing to realize a general and useful procedure for highly practical enantioselective synthesis of structurally diverse natural and unnatural α-alkyl-α-amino acids as well as α,α-dialkyl-α-amino acids. This approach is successfully applied to the short asymmetric synthesis of cell adhesion BIRT-377. 相似文献
12.
Kazuhiko Sakaguchi 《Tetrahedron》2003,59(34):6647-6658
Cationic rearrangement of several α-hydroxysilanes is described. Treatment of both (1R,1′R,2′S)-α-hydroxycyclopropylsilane syn-9 and (1S,1′R,2′S)-anti-9 under aqueous H2SO4 underwent rearrangement via a common α-silyl cation intermediate A to give a mixture of the ring-opened (R)-vinylsilane 13, the tandem [1,2]-CC bond migration product (1R,2S,1′R)-14, and its 1′S isomer 15. On the other hand, the acidic treatment of (R,E)-α-hydroxyalkenylsilane 8 or (R,Z)-8 was each accompanied with partial racemization to give an enantiomeric isomer of allylic alcohol 23 via a preferential syn-facial SN2′ reaction, respectively. Both α-hydroxyalkynylsilane 6 and α-hydroxyalkylsilane 12 were inert to the acidic conditions; however, treatment of (R)-α-mesyloxyalkynylsilane 26 under aqueous H2SO4 gave a mixture of the optically active rearranged allene 27, α,β-unsaturated ketone 28, and (S)-α-hydroxyalkynylsilane 6 with partial racemization. Comparisons of the reactivities of these α-hydroxysilanes under acidic conditions are also disclosed. 相似文献
13.
Thermolysis of substituted methyl 1-methyleneamino-4,5-dioxo-4,5-dihydro-1H-pyrrole-2-carboxylates 2a,b led to substituted dimethyl 3,9-dioxo-1,5,7,11-tetrahydro-1H,7H-dipyrazolo[1,2-a;1′,2′-d][1,2,4,5]tetrazine-1,7-dicarboxylates 4a,b and methyl 2,5-dihydro-5-oxo-1H-pyrazole-3-carboxylates 5a,b as minor products. The structure of compound 4a was determined by X-ray crystallography. The proposed mechanism of this conversion includes generation of (N-methyleneamino)imidoylketenes 6a,b and its intramolecular transformation to azomethine imines—5-oxo-2,5-dihydropyrazole-1-methylium-2-ides 7a,b, which undergo dimerization in head-to-tail manner yielding products 4a,b and partially hydrolyse to compounds 5a,b. 相似文献
14.
Guanghui Deng Yuanyuan Li Yu Zhou Jiang Wang Hualiang Jiang Hong Liu 《Tetrahedron》2008,64(46):10512-10516
The non-proteinogenic amino acid (2S)-2-amino-3,3-bis(4-fluorophenyl)propanoic acid [(S)-1] is a key intermediate required for the synthesis of Denagliptin (2a). Denagliptin is a dipeptidyl peptidase IV (DPP IV) inhibitor that is being developed for the treatment of type-2 diabetes mellitus. A diastereoselective, cost-efficient synthetic procedure for (S)-1 was developed by alkylating a Ni(II) glycine equivalent derived from (S)-2-[(N-benzylprolyl) amino] benzophenone [(S)-BPB]. The alkylated product was then decomposed to isolate the target amino acid (S)-1 (ee >99%) and ligand (S)-BPB, which can be reused in subsequent reactions. The enantiomer (R)-1 and racemate (rac)-1 were synthesized from their corresponding Ni(II) glycine equivalents. Denagliptin diastereomers (2), derived from the key intermediates (S)-1, (R)-1, and (rac)-1 were synthesized, and their dipeptidyl peptidase IV inhibitory activities were investigated. These findings are important in the design and synthesis of DPP IV inhibitors. 相似文献
15.
Yoshikazu Hiraga Triana WidiantiTsuyoki Kunishi Manabu Abe 《Tetrahedron: Asymmetry》2011,22(2):226-237
Novel β-homoproline derivatives, 2-hydroxy-2-(pyrrolidin-2-yl)acetic acids (R,S)- and (S,S)-1a-d, were synthesized. All of the prepared compounds were used as organocatalysts in the direct asymmetric aldol reaction of 4-nitrobenzaldehyde with several ketones. Among these catalysts, (R)-2-hydroxy-2-((S)-pyrrolidin-2-yl)acetic acid (R,S)-1a showed good catalytic ability in the formation of aldol product 13 (up to 69% ee, 95% yield), which was similar to the results catalyzed by l-proline (71% ee, 96% yield). Relatively low yields and low enantioselectivities were observed in aldol reactions catalyzed by (S,S)-1a, for example, 13 was obtained in 55% yield and 13% ee. The aldol reaction catalyzed by the methyl-protected carboxylic acid 1b and esters 1c,d produced much lower chemical yields and enantioselectivities during the formation of 13. The cooperative effect of the (R)-configured hydroxyl group and the carboxyl group was found to play an important role in inducing enantioselectivity in the aldol reaction. Relatively high diastereoselectivities (anti:syn = 85:15) and enantioselectivity (anti, 83% ee) were observed in the aldol reactions of 4-nitrobenzaldehyde with cyclohexanone, which was catalyzed by (R,S)-1a. 相似文献
16.
The synthesis of (4R,8R)- and (4S,8R)-4,8-dimethyldecanal 1 and 1a has been achieved connecting the chiral building block (R)-2-methyl-1-bromobutane 4 with (R)- and (S)-citronellol derivatives. The key intermediate 4 was obtained optically pure in five steps from methyl (S)-3-hydroxy-2-methylpropionate 2. 相似文献
17.
A new self-assembled catalyst based on titanium complex has been developed for the effective enantioselective cyano-ethoxycarbonylation of aldehydes. The self-assembled catalyst was readily prepared from (R)-3,3′-bis((methyl((S)-1-phenylethyl)amino)methyl)-1,1′-binaphthyl-2,2′-diol (1h), N-((1S,2R)-2-hydroxy-1,2-diphenylethyl)acetamide (2b), and tetraisopropyl titanate (Ti(OiPr)4). A variety of aromatic aldehydes, aliphatic aldehydes, and α,β-unsaturated aldehydes were found to be suitable substrates in the presence of the self-assembled titanium catalyst (5 mol % 1h, 5 mol % 2b, and 5 mol % Ti(OiPr)4). The desired cyanohydrin ethyl carbonates were afforded with high isolated yields (up to 95%) and moderate to good enantioselectivities (up to 92% ee) under mild conditions (at −15 °C). A possible catalytic cycle based on the experimental observation was proposed. 相似文献
18.
Giuseppe BorsatoOttorino De Lucchi Fabrizio FabrisVittorio Lucchini Pietrogiulio FrascellaAlfonso Zambon 《Tetrahedron letters》2003,44(17):3517-3520
The resolution by Lipase PS of rac-5 (from reduction of ketone 6, obtained from dicyclopentadiene with a new environment-friendly synthesis) gives (2S)-5, which was further reduced to the endo(2R)-1a alcohol. The endo(2S)-1b alcohol was obtained from camphor with a multistep synthesis. Pinacol couplings of 3a,b, carried out with Mg/Hg or Corey's general procedure respectively, afforded with high diastereoselectivity the C2 symmetry diols (2R,2′R)-2a and (2S,2′S)-2b, with endo oriented OH functions. The enantiogenic power of the endo alcohol (2R)-1a and (2S)-1b and of the diols (2R,2′R)-2a and (2S,2′S)-2b was tested towards the LiAlH4 reduction of acetophenone. The C2 symmetry appears to play a fundamental role. 相似文献
19.
Through ring-closure reactions of N- or 1′-substituted 1-(2′-aminoethyl)-6,7-dimethoxy-1,2,3,4-tetrahydroisoquinolines (5a-e) with phenylphosphonyl dichloride, 1- or 3-substituted 4-phenyl-1,3,4,6,7,11b-tetrahydro-2H-1,3,2-diazaphosphorino[6,1-a]isoquinolin-4-one diastereomers (7a-e and 8a-c,e), the first representatives of a new ring system, were prepared. The diastereomeric ratios in the cyclizations and the conformer (A-E) populations of the nitrogen-bridged tricyclic systems (7 and 8) were strongly influenced by the N- and 1′-substituents of the starting diamines. The conformational analysis of compounds 7 and 8 was performed by 1H, 13C and 31P NMR methods. 相似文献
20.
The high-pressure asymmetric Diels-Alder reactions of d-galacto- (1a) and d-manno-3,4,5,6,7-penta-O-acetyl-1,2-dideoxy-1-nitrohept-1-enitol (1b) with 2,5-dimethylfuran (2) afforded mixtures of cycloadducts, from which the (2S,3R)-3-exo-nitro (3a and 3b), (2R,3S)-3-exo-nitro (4a and 4b), and (2R,3S)-1′,2′,3′,4′,5′-penta-O-acetyl-1′-C-(1,4-dimethyl-3-endo-nitro-7-oxabicyclo[2.2.1]hept-5-en-2-exo-yl)-d-galacto-pentitol (5b) were isolated pure. Deacetylation of these compounds led to new chiral mono-, bi-, and tricyclic ethers, being their asymmetric centers arising from the chiral inductor used in the cycloaddition reaction. A ring opening mechanism through a 1-nitro-1,3-cyclohexadiene intermediate has been proposed. 相似文献