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1.
Stapled helical l-leucine-based heptapeptides were synthesized and used as catalysts for the enantioselective epoxidation of α,β-unsaturated ketones. All N-terminal free stapled peptides were successfully used as chiral catalysts. Among them, the use of H-hS3,7hS-10 gave epoxide products with high enantioselectivities of up to 99% ee. Furthermore, the dominant conformations of the N-terminal protected stapled peptides R3,7R-10 and hS3,7hS-10 were investigated by 1H NMR, IR, CD spectra, and X-ray crystallographic analysis. The peptide R3,7R-10 formed a right-handed (P) α-helix in solution and in the crystalline state, while hS3,7hS-10 formed a right-handed (P) 310-helix in solution.  相似文献   

2.
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   

3.
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   

4.
Enantiomerically pure 2,8-diazabicyclo[3.2.1]oct-2-ene derivatives (+)-5 and (−)-5 have been obtained from 2-azido-3-tosyl-7-azabicyclo[2.2.1]heptanes (+)-1 and (−)-2 and their enantiomers, by ring expansion under radical conditions. Compounds (+)-5 and (−)-5 were transformed into hemiaminals 9 ((3S,4R,5R)- and 10 ((3R,4S,5S)-5-(2-aminoethyl)-2,3,4-trihydroxypyrrolidine) that are good inhibitors of α-mannosidases.  相似文献   

5.
(1R,2S,3S,5R,7aR)-1,2-Dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine[(−)-3-epihyacinthacine A5, 1a] and (1S,2R,3R,5S 7aS)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine[(+)-3-epihyacinthacine A5, 1b] have been synthesized either by Wittig's or Horner-Wadsworth-Emmond's (HWE's) methodology using aldehydes 4 and 9, both prepared from (2S,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (2, partially protected DADP), and the appropriate ylides, followed by cyclization through an internal reductive amination process of the resulting α,β-unsaturated ketones 5 and 10, respectively, and total deprotection.  相似文献   

6.
Enantioenriched tertiary homoallylic alcohol derivatives (S)-2c and (S)-2a were obtained via Evans aldol methodology and enzymatic resolution of racemic tertiary acetate 2e, respectively. In order to study asymmetric 1,3-induction of the stereogenic center present in 2, congener (R)-2a as well as its O-protected derivatives (R)-2b-d were submitted to Sharpless asymmetric dihydroxylation to yield the diastereomeric 1,2,4-triol derivatives (2R,4R)- and (2S,4R)-3a-d, revealing that neither the substrate nor the Sharpless catalyst exert any stereocontrol. Similar observations were made for the less bulky alkynyl-substituted derivative 12b. However, by using a directed dihydroxylation, the anti product (2R,4R)-3a was favored.  相似文献   

7.
Machiko Ono  Yuki Shida 《Tetrahedron》2007,63(41):10140-10148
(±)-(4,5-anti)-4-Benzyloxy-5-hydroxy-(2E)-hexenoic acid 6 was subjected to δ-lactonization in the presence of 2,4,6-trichlorobenzoyl chloride and pyridine to give the α,β-unsaturated-δ-lactone congener (±)-7 (87% yield) accompanied by trans-cis isomerization. This δ-lactonization procedure was applied to the chiral synthesis of (+)-(4S,5R)-7 or (−)-(4R,5S)-7 from the chiral starting material (+)-(4S,5R)-6 or (−)-(4R,5S)-6. Deprotection of the benzyl group in (+)-(4S,5R)-7 or (−)-(4R,5S)-7 by the AlCl3/m-xylene system gave the natural osmundalactone (+)-(4S,5R)-5 or (−)-(4R,5S)-5 in good yield, respectively. Condensation of (−)-(4R,5S)-5 and tetraacetyl-β-d-glucosyltrichloroimidate 22 in the presence of BF3·Et2O afforded the condensation product (−)-8 (97% yield), which was identical to tetra-O-acetylosmundalin (−)-8 derived from natural osmundalin 9.  相似文献   

8.
The organotin (IV) derivatives of 2-mercapto-4-methylpyrimidine (Hmpymt) R3SnL (R = Ph 1, PhCH22, n-Bu 3), R2SnClmLn (m = 1, n = 1, R = CH34, Ph 5, n-Bu 6, PhCH27; m = 0, n = 2, R = CH38, n-Bu 9, Ph 10, PhCH211) were obtained by the reaction of the organotin(IV) chlorides R3SnCl or R2SnCl2 with 2-mercapto-4-methylpyrimidine hydrochloride (HCl · Hmpymt) in 1:1 or 1:2 molar ratio. All complexes 1-11 were characterized by elemental analyses, IR, 1H, 13C and temperature-dependent 119Sn NMR spectra. Except for complexes 3 and 6, the structures of complexes 1, 2, 4, 5, 7, 8-11 were confirmed by X-ray crystallography. Including tin-nitrogen intramolecular interaction, the tin atoms of complexes 1-7 are all five-coordinated and their geometries are distorted trigonal bipyramidal. While the tin atoms of complexes 8-11 are six-coordinated and their geometries are distorted octahedral. Besides, the ligand adopts the different coordination modes to bond to tin atom between the complexes 1, 6, 7 and 2, 3, 4, 5, 8-11. Furthermore, intermolecular Sn?N or Sn?S interactions were recognized in crystal structures of complexes 4, 7 and 11, respectively.  相似文献   

9.
In this study, the crystal structures of the dispiroansa spermine derivatives of cyclotriphosphazene are characterised for the first time. The reaction of spiro-, gem-disubstituted cyclotriphosphazene derivatives, N3P3Cl4R2 [R = NHPh, (HN(CH2)3NH)0.5, (OCH2C(CH3)2CH2O)0.5], (13), with spermine (4), in aprotic solvents such as CH2Cl2 results in a series of dispirobino spermine derivatives of cyclotriphosphazene (5a, 6a, 7), namely spermine bridged compounds. Whereas, in protic solvents such as CHCl3 give, dispiroansa derivatives (810) namely tetracyclic cyclotriphosphazene. The new series of dispirobino and dispiroansa spermine derivatives of cyclotriphosphazene (5a, 6a, 710) have been characterised by elemental analysis, mass spectrometry, X-ray (for 5a, 8, 10) and 1H, 31P NMR spectroscopies.  相似文献   

10.
Both racemic ethyl 5-iodo-2-methylcyclohexanecarboxylate (1), known as Mediterranean fruit fly attractant ceralure B1, and its (−)-(1R,2R,5R) enantiomer 1a were conveniently synthesized from commercially available racemic trans-6-methyl-3-cyclohexenecarboxylic acid 2 or its (1R,6R) enantiomer 2a. Key steps included an asymmetric Diels-Alder reaction using a sultam auxiliary and cyclization of the unwanted trans-5-iodo-trans-2-methylcyclohexanecarboxylic acid (8) to the intermediate lactone 7 (or 8a to 7a). The new method may circumvent chromatographic separations and seems amenable to scale-up.  相似文献   

11.
In HF-SbF5, quinidine 1a or its dihydrochloride cyclises previously obtained with usual acids. A similar reaction is observed in the presence of CCl4. Under similar conditions quinidine acetate 1b and epiquinidine acetate 2b dihydrochlorides both yield 10,10-difluoro derivatives epimeric at C-3, 6 and 7, and 9c and 10b, and a rearranged difluoro derivative 8b and 11b, respectively. Epiquinidine 2a leads to the expected analogues 10a and 11a and to a ketone 9a. Formation of gem-difluoro compounds implies chloro intermediates at C-10, precursors of α-chlorocarbenium ions, which are trapped by a fluoride ion and which lead by halogen exchange to the products.  相似文献   

12.
The readily available 3-O-benzyl-1,2-O-isopropylidene-β-d-fructopyranose (2) was transformed into its 5-O- (3) and 4-O-benzoyl (4) derivative. Compound 4 was straightforwardly transformed into 5-azido-4-O-benzoyl-3-O-benzyl-5-deoxy-1,2-O-isopropylidene-β-d-fructopyranose (7) via the corresponding 5-deoxy-5-iodo-α-l-sorbopyranose derivative 6. Cleavage of the acetonide in 7 to give 8, followed by regioselective 1-O-silylation to 9 and subsequent catalytic hydrogenation gave a mixture of (2S,3R,4R,5R)- (10) and (2R,3R,4R,5R)-4-benzoyloxy-3-benzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine (12) that was resolved after chemoselective N-protection as their Cbz derivatives 11 and 1a, respectively. Stereochemistry of 11 and 1a could be determined after total deprotection of 11 to the well known DGDP (13). Compound 2 was similarly transformed into the tri-orthogonally protected DGDP derivative 18.  相似文献   

13.
Fanhong Wu  Fanhua Xiao  Yongjia Shen 《Tetrahedron》2006,62(43):10091-10099
Sodium dithionite initiated free-radical addition of polyfluoroalkyl iodides (2m-2s) with norbornene 1a and its derivatives, such as norbornene-2-carboxylates 1b and 1c, and norbornene-2-carboxylic acids 1d and 1e was investigated. In all the cases, the addition of RF group was stereoselectively delivered at exo-position and the predominant configuration of products was trans. Under the similar condition, norbornene-2-carboxylic ethyl ester 1b reacted with 2p to give 6-exo-RF-5-endo-iodo adduct 3bp and 5-exo-RF-6-endo-iodo adduct 5bp in the ratio of 4:1. While 1c, which has a heavy crowded group in the 2-endo-position, gave 6-exo-RF-5-endo-iodo adduct 3cp and polyfluoroalkylated product 4cp retaining the trans-configuration and the exo-orientation of RF group. The fluoroalkylation-lactonization reaction occurred in the reaction of norbornene-2-endo-carboxylic acids 1d and 1e with polyfluoroalkyl iodides to afford the corresponding fluoroalkylated γ-lactone products (7dp-7ds, and 7em-7er). The configuration of the products was further confirmed by 2D NMR and X-ray diffraction analyses for the first time.  相似文献   

14.
Eight new organotin (IV) carboxylates, (R3Sn)4(nap)4 (R = Me 1, n-Bu 2), [(R3Sn) (nap)]n (R = Ph 3, PhCH24), (R2Sn) (nap)2 (R = n-Bu 5, Ph 6, PhCH27) and {[R2Sn(nap)]2O}2 (R = Me 8) (nap = (S)-(+)-6-methoxy-α-methyl-2-naphthaleneaceto anion) have been synthesized. All of the complexes have been characterized by elemental analysis, FT-IR, NMR (1H, 13C and 119Sn) spectra. Among these complexes, complexes 1, 3, 5 and 8 were also characterized by X-ray crystallography diffraction analysis, and the data of X-ray crystallography diffraction indicated that complexes 1, 3 and 5 are new chiral organotin (IV) carboxylates complexes. The structural analyses show that complex 1 has a tetranuclear Sn4O8 macrocycle structure, complex 3 has a 1D spring-like chiral helical chain with a columnar channel, complex 5 possesses a dimer structure, and complex 8 has a supramolecular chainlike ladder structure through weak intermolecular non-covalent OO interactions.  相似文献   

15.
d- and l-Serine have been used for the enantioselective synthesis of tosylates 7a and 7b, useful building blocks for the synthesis of triols 5a and 5b which have already been obtained via a diastereoselective synthesis and used for the synthesis of 2a, 2b and 2c. We have thus performed a formal synthesis of 24S,25-(OH)2-D3, 24R,25-(OH)2-D3 and 1α,24R,25-(OH)3-D3.  相似文献   

16.
A novel solid-phase method for the synthesis of 4-methyl-pyrido[2,3-d]pyrimidin-7-one compounds with two diversity points is described. The polymer supported methylsulfonyl derivatives A3, achieved by coupling compound G with different resin-bound amines A1 followed by oxidation with MCPBA, are substituted with several amines R1R2NH. Final cleavage affords 126 compounds having formula H in good yield and purity.  相似文献   

17.
Naturally occurring (1S,2R,3R,5R,7aR)-1,2-dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine [(+)-hyacinthacine A6, 2] together with unnatural (1S,2R,3R,7aS)-1,2-dihydroxy-3-hydroxymethylpyrrolizidine [(+)-7a-epi-hyacinthacine A1, 3] and (1S,2R,3R,5S,7aS)-1,2-dihydroxy-3-hydroxymethyl-5-methylpyrrolizidine [(+)-5,7a-diepi-hyacinthacine A6, 4] have been synthesized from a DALDP derivative [5, (2R,3S,4R,5R)-3,4-dibenzyloxy-2′-O-tert-butyldiphenylsilyl-2,5-bis(hydroxymethyl)pyrrolidine], as the homochiral starting material. The synthetic process employed took advantages of Wittig methodology followed by internal lactamization, in the case of (+)-7a-epi-hyacinthacine A1 (3), and reductive amination for (+)-hyacinthacine A6 (2) and (+)-5,7a-diepi-hyacinthacine A6 (4).  相似文献   

18.
Yuji Takashima 《Tetrahedron》2010,66(1):197-2519
A general approach to the (S)- and (R)-isoflavans was invented, and efficiency of the method was demonstrated by the synthesis of (S)-equol ((S)-3), (R)-sativan ((R)-4), and (R)-vestitol ((R)-5). The key step is the allylic substitution of (S)-6a (Ar1=2,4-(MeO)2C6H3) and (R)-6b (Ar1=2,4-(BnO)2C6H3) with copper reagents derived from CuBr·Me2S and Ar2-MgBr (7a, Ar2=4-MeOC6H4; 7b, 2,4-(MeO)2C6H3; 7c, 2-MOMO-4-MeOC6H3), furnishing anti SN2′ products (R)-8a and (S)-8b,c with 93-97% chirality transfer in 60-75% yields. The olefinic part of the products was oxidatively cleaved and the Me and Bn groups on the Ar1 moieties was then removed. Finally, phenol bromide 9a and phenol alcohols 9b,c underwent cyclization with K2CO3 and the Mitsunobu reagent to afford (S)-3 and (R)-4 and -5, respectively.  相似文献   

19.
PN ligands 3 and 4, derived from 2-diphenylphosphanylmethylpyridine 2a, were synthesized, to which in the backbone a tether to a cyclopentadiene system and for comparison an iPr substituent were attached. The chiral compounds were resolved by introduction of a menthoxy substituent into the 2-position of the pyridine system and/or palladium complexes with enantiomerically pure co-ligands. The tripod ligand 3b contains three different binding sites (Cp, P, N) connected by a resolved chiral carbon atom. (SC)-configuration of this tripod ligand enforces (RRh)-configuration at the metal atom in the halfsandwich rhodium complex (LMent,SC,RRh)-7b. The opposite metal configuration is inaccessible. Substitution of the chloro ligand in (LMent,SC,RRh)-7b by halide (Br, I) or pseudohalide (N3, CN, SCN) ligands occurs with retention of configuration to give complexes 8b-11b. However, in the reaction of (LMent,SC,RRh)-7b with PPh3 the pyridine arm of the tripod ligand in compound 13b becomes detached from the metal atom. In the Cp*Rh and CpRh compounds of the bidentate PN ligands 4a and 4b both metal configurations are accessible and in complexes 14a-17a and 14b-17b they equilibrate fast. The stereochemical assignments are corroborated by 9 X-ray analyses.  相似文献   

20.
Shao-Feng Wu 《Tetrahedron》2010,66(9):1653-346
The SmI2-mediated and H2O-promoted reductive cross-coupling reactions of the l-tartaric acid derived nitrone (3S,4S)-8 with aldehydes/ketones, and the l-malic acid derived nitrone (S)-6 with aliphatic acyl chlorides have been investigated, respectively. (2R,3S,4S)-1,3,4-Trihydroxyprolinol derivatives 9a-f were obtained with high C-2/C-3 trans-selectivities, and 72:28-85:15 diastereoselectivities at the carbinol center from aromatic ketones/aldehydes, while low diastereoselectivities for aliphatic aldehydes. Conditions have been established for the syntheses of (2R,3S,4S)-3,4-dihydroxyprolinol derivatives such as 18, by N-O bond cleavage of the corresponding N-hydroxyprolinol derivatives 9b-f, or more conveniently by a one-pot reductive coupling of nitrone 8 and in situ N-O bond cleavage of the resultant coupling product. The 2-acyl-3-benzyloxy-1-hydroxypyrrolidines 10a-f were formed in 48-82% yields, and in 74:26-78:22 diastereoselectivities. It was revealed that the amount of water required for the reaction is substrate-depending.  相似文献   

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