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1.
The protection of uracil and 2-N-acyl guanine residues with 4-O-phenyl [or 4-O-(2,4-dimethylphenyl)] and 6-O-(2-nitrophenyl) groups as in 7a [or 7b] and 9, respectively, is described. These O-aryl protecting groups, which appear to withstand the usual conditions of oligonucleotide synthesis, may readily be removed by treatment with 2-nitrobenzaldoximate ions.  相似文献   

2.
A new purine derivative with cytokinin activity was isolated from the cuckoo-pint fruits (Zantedeschiaaethiopica) and identified as 6-(o-hydroxybenzylamino)-2-methylthio-9-β-D-glucofuranosylpurine 1.  相似文献   

3.
X-Ray and 1H N.M.R. studies on pyranoid rings 1,2-cis-fused to dioxolane rings in acetylated D-gluco- and D--galactopyranose derivatives demonstrate that the configuration of the dioxolane ring influences the conformation of the pyranoid ring in the D-gluco but not in the D-galactopyranose series. The crystal structure of 3,4,6-tri-O-acetyl-1,2-O-(R)--(l-cyano-ethylidene)-α-D-glucopyranose (1) and 3,4,6-tri-O-acetyl-1,2-O-(R)-(1-cyano-ethylidene)-α-D-galactopyranose (2)have been determined by X-ray analysis. Lattice parameters for 1 are a=20.6021 (11), b=8.0438 (2), c=5.5541 (1) Å and β= 95.588 (3)° for a cell with P21 symmetry. These parameters for 2 are a=20.3361 (7), b=10.0907 (2), c=18.9115 (5) Å, β =112.399 (2)°, C2, with two crystallographycally independent molecules. The conformation of the pyranoid ring in both compounds can be described as flattened 4C1 and that of the dioxolane ring as distorted E1. The importance of the torsion angles for describing problems of configuration is remarked and the use of relative configurational angles is stressed. The 1H N.M.R. spectra of 1 and 2 and 3,4,6-tri-O-acetyl-1,2-O-(S)- and (R)-ethylidene-α-D-glucopyranose (5 and 7), 3,4,6-tri-O-acetyl--1,2-O-(S)- and (R)-ethylidene-α-D-galactopyranose (6 and 8), and 3,4,6-tri-O-acetyl-1,2-O-(S)-and (R)-benzylidene-α-D-glucopyranose (9 and 10) have been analyzed by using iterative computer methods and N.O.E. measurements. The results indicate that the major solution conformation of the pyranoid ring of the derivatives in the D-gluco series 1, 5 and 9 may be described as flattened 4C1 and that of 7 and 10 as 2S5. The major solution conformation of the pyranoid ring in all compounds in the D-galacto series (2,4,6,8) may be described as flattened 4C1.  相似文献   

4.
A large scale synthesis for (-)-3-PPP has been developed. The racemic methoxy compound 1 was prepared in a three step procedure in 63% yield. This was resolved as a diastereomeric salt by crystallization of the (-)-di-p-toluoyltartrate. Two crystallizations gave the pure (-)-enantiomer 2 in 50% of the theoretical yield and with an enantiomeric excess of >95%. Demethylation using aqueous HBr gave (-)-3-PPP, (3). Compound 2 was also prepared in a stereoselective synthesis from S-(-)- N-propyl-2- chloromethylpyrrolidine 4. By X-ray crystallography it was shown that (-)-3-PPP has the S-configuration at the chiral carbon.  相似文献   

5.
Cycloalkylation of dimethyl malonate and tosylmethylisocyanide with cis,cis-1,9-dibromonona-2,7-diene has demonstrated the feasibility of direct cyclization as a route to functionalized cis,cis-1,6-cyclodecadienes.  相似文献   

6.
Although the hydrochloride of c-4-t-butyl-1-phenyl-c-1-(N-piperidyl)cyclohexane crystallizes in the conformation with axial t-butyl, it exists as an almost equimolar mixture of the two chair conformers in CD2 Cl2 solution. The position of equilibrium allows one to calculate ΔG°t-Bu as ?4.9 kcal/mol.  相似文献   

7.
The cis-cxo- amino acid c with norbornene skeleton was converted into 2-aryvl-cis-cxo-1,3-oxazin-4-ones 5a-d. These compounds, similarly to the diendo isomers 1a-d studied by us earlier, undergo retrodiene decomposition under mild conditions to give 2-aryl-62-l,3-oxazin-6-ones (2a-d) in 50-60% yield. The ratio of the decomposition rate constants of the tricyclic diendo and diexo-1,3-oxazin-4-ones, measured in toluene solution, is about 2.  相似文献   

8.
Practical procedures for the resolution of racemic modification of (1R, 2S)-and (1S, 2R)-1-amino-2-ethylcyclopropane-1-carboxylic acid 1a,b,(1R, 2S)- and (1S, 2R)-1-amino-2-methylcyclopropane-1-carboxylic acid 2a,b, and (1R, 2R)- and (1S, 2S)-1-amino-2-methylcyclopropane-1-carboxylic acid 3a,b are described; the structures as 1a,2a, and 3a were confirmed by X-ray-crystallographic methods.  相似文献   

9.
《Tetrahedron》1986,42(8):2193-2201
The biogenetic-type asymmetric synthesis of limonene and bisabolenes is described. As model studies for the present asymmetric synthesis, the cyclization of catechol, biphenol and binaphthol mononeryl ethers 1, 4, and 5, with organoaluminum reagents are executed to furnish limonene as a major product. Since the reaction of 1, 4, and 5 has proved to proceed much faster than that of neryl phenyl ether under the similar conditions, the rate acceleration is attributed to the novel metal-anchimeric assistance of the aluminum reagents bound with the neighboring hydroxyl group for effecting the generation of the allyl cation. This anchimeric effect is utilized for the enantioselective cyclization of (R)-(+)-1,1'-bi-2-naphthol mononeryl ether (8) upon treatment with modified aluminum reagent 9 to produce limonene with high optical purity (77% ee). In a similar fashion, (R)-(+)-binaphthol (Z,Z)-mono-farnesyl ether 16a undergoes the enantioselective cyclization to give β-bisabolene in 76% ee.  相似文献   

10.
Lithiation of both (Z)- and (E)-3-trimethylsilyl-2-propenyl N,N-diisopropyl carbamate 2 affords the (2E) -lithium compound 3. Aluminium- or titanium-mediated addition to aldehydes, 4 gives (1E)-(3R*4S*)-enol carbamates 7. A stereospecific Peterson elimination (borontriflouride- or base-mediated) introduces the second double bond either with (3E)- or with (3Z)-configuration. So just by reagent selection for each of the two steps, (1E,3E)-, (1E,3Z)-, (1Z,3E)-, or (1Z,3Z)- dienes 8 - 11, respectively, are prepared with stereoselectivities up to > 99.7%  相似文献   

11.
diendo- and diexo-2-Methylamino and 2-benzylamino-3-hydroxymethylbicyclo [2.2.1]heptanes and the corresponding bicycio [2.2.1] heptenes (5a -d, 7a -d) were synthesized from β-amino acid esters containing the norbornane or norbornene skeleton (3a-d). The aminoalcohols were converted to 5,8- methano -3,1-benzoxazines by reaction with formaldehyde. As established by 1H and 13C NMR spectroscopy, the predominant conformation is endo - boat (B) for the diexo, and exo - boat (E) for the diendo derivatives.  相似文献   

12.
In deprotonation studies with isomerically pure erythro-3 and threo-3, “retro-Wittig” reaction was only detected for erythro-3. Mixtures of erythro-3 and threo-3, under lithium salt-free conditions, undergo stereochemical drift because of synergism between diastereomeric oxaphosphetanes cis-2 and trans-2 during their decomposition to alkenes.  相似文献   

13.
Unlike unsubstituted perfluoropropene [1,2] 1-(2-tetrahydrofuryl)-pentafluoropropene 1 reacts with sodium alkoxides in parent alcohol solutions to give 1-alkoxy-1-(2-tetrahydrofuryl)-tetrafluoropropenes 2 as major products and 1-alkoxy-2H-1-(2-tetrahydrofuryl)-pentafluoropropanes 3 as very minor products. The yield of adducts 3 is, to some extent, increased by the reduced basicity of the alkoxide ion. Results are discussed in terms of the supposed properties of the carbanionic intermediates involved.N.m.r., m.s., and i.r. data for, and some chemical properties of compounds 2, viz., further reactions with sodium alkoxides and hydrolysis are described.  相似文献   

14.
Direct chlorination of 2-(2H-hexafluoropropyl)-tetra- hydrofuran 1 gave high yield of 2-(2-chlorohexafluoropropyl)- pentachloro-2,5-dihydrofuran 2. Bromination of 1 gave very complex mixture of products, from which three compounds, viz. 2-bromo-5-(2H-hexafluoropropyl)-furan 3, 3-bromo-5-(2H-hexafluoropropyl)-furan 4, and 2,4-dibromo-5-(2H-hexafluoropropyl)furan 5 were isolated. Exchange fluorination of 2 with dry KF at 240 – 300° led to a stepwise substitution of fluorines for chlorines to give mixtures of chloro-fluoro-2-(2-chlorohexafluoropropyl)-dihydrofurans 7,8,9 and 10, together with small amounts of 2-(2-chlorohexafluoropropyl)-3,4,5-trichlorofuran 6.Exchange fluorination of 3,4-dihalo-2,2,5,5-tetrafluoro- 2,5-dihydrofurans 11a and 11b led to a substitution of fluorine for one vinylic halogen to give 3-halo-2,2,4,5,5-pentafluoro-2,5-dihydrofurans 12a and 12b in good yields.Compounds 212 were characterised by n.m.r., m.s., and i.r. spectroscopy and elemental analysis.  相似文献   

15.
4-Fluoro-2-(F-ethyl)-3-(F-methyl)-1, 5-benzoxazepine was prepared by reaction of F-2-methyl-2-pentene with 2-aminophenol in the presence of triethylamine in diethyl ether. The reaction of F-2,4-dimethyl-3-heptene with 2-aminophenol in dimethylformamide gave 7-(F-1-methylethyl)-8- (F-ethyl)-9,14-benzoxazepino[4,3-b]1,6-benzoxazepine. Several ortho-bifunctional benzenes reacted similarly with F-2-methyl-2-pentene and F-2,4-dimethyl-3-heptene to give the corresponding seven-membered benzoheterocycles.  相似文献   

16.
《Tetrahedron》1986,42(8):2345-2350
In the reactions of 2-thioxo-cis- and trans-3,1-perhydrobenzoxazines (3, 4) with methyl iodide the hydrogen iodide formed in the S-methylation process brings about ring-opening and gives iodomethylthiolcarbamates (7, 8). Under similar conditions, the thioether salts (15, 16) of the structurally isomeric cis- and trans-2-thioxo-1,3-perhydrobenzoxazines, corresponding to the unstable intermediates in the former reactions, are stable. Under more vigorous conditions, the cis isomer thioether salt 15 is transformed into the corresponding cis-and trans-l,3-perhydrobenzoxazin-2-ones (17, 18) by ring-opening and subsequent ring-closure, whereas the trans isomer 16 gives only trans-1,3-perhydrobenzoxazin-2-one (18).  相似文献   

17.
The cyanohydrin of methyl perfluoroheptyl ketone 2 was able to be synthesized by a two-step process, i.e., an addition of sodium bisulfite and subsequent treatment with sodium cyanide. When equimolar amounts of ketone 2 and sodium cyanide were reacted in water or dipolar aprotic solvent such as dimethyl-formamide, acetonitrile, 1,2-dimethoxyethane and tetrahydrofuran, cyclic addition products composed of two molecules of ketone 2 and one molecule of hydrogen cyanide were exclusively formed as 2,5-dimethyl-2,5-bis(perfluoroheptyl)-4-oxazolidone 6 and 2,5-dimethyl-2,5-bis(perfluoroheptyl)-1,3-dioxolane-4-one 7 instead of the cyanohydrin of ketone 2. It is conceivable that a solubility characteristic of a compound carrying a long perfluoroalkyl group is responsible for the exclusive formation of cyclic compounds 6 and 7  相似文献   

18.
The cis- and trans-2-amino-4-cyclohexene-1-carboxylic acids 1 and 3 react with imidates to give the condensed-skeleton, bicyclic cis- and trans-pyrimidin-4-ones 8 and 9. The amino acids 1 and 3 were reduced to the cis-and trans-1, 3-aminoalcohoIs 6 and 7, which were cyclized by means of imidates to the bicyclic tetrahydro-4H-3,1-benzoxazines 10 and 11, or were converted, via the corresponding carbamates 14 and 15 into the tetrahydro-4H-3,1-benzoxazin-2(1H)-ones 16 and 17. The 2-thioxo analogues 18 and 19 were prepared by cyclization of the dithiocarbamates obtained from the aminoalcohols 6 and 7 by treatment with carbon disulphide. The trans-aminoalcohol 7 and its saturated analogue reacted with p-chlorobenzaldehyde to furnish the hexahydro 13 and octahydro-4H-3,1-benzoxazine 13a, respectively. 1H and 13C NMR studies showed that, similarly to the earlier-investigated analogues containing oxygen or unsubstituted nitrogen at position 1, the synthesized cis isomrs 8, 10, 16 and 18 occurred as the preferred conformer in the heterocyclic twist inverse form of N-inside type (quasiaxial C6-N bond) (B). In the trans isomers containing a saturated C-2 atom (13 and 13a), H-2 and H-6 are in cis relative positions.  相似文献   

19.
Preparation of potential insect antijuvenile hormone agents 2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2H-chromene (3a), 6-methoxy-2,2-dimethyl-7-(2,2,2-trifluoroethoxy)-2H-chromene (3b) and 7-methoxy-2,2-dimethyl-6--(2,2,2-trifluoroethoxy)-2H-chromene (3c) and the corresponding 3,4-epoxides 5a and 5b is reported.  相似文献   

20.
Flow vacuum thermolysis (FVT) of thiophene-2,3-dicarboxylic anhydride (2) in the presence of 2,3-dimethylbutadiene (6) gives, in addition to 5,6-dimethylthianaphthene (9). small quantities of a dihydrodimethylthianaphthene (12) and another dimethylthianaphthene (13) which is probably also formed by dehydrogenation of 12 with chloranil. The partial structures of these minor products are consistent with their being formed by a [2+2]-cycloaddition between 6 and an intermediate aryne, 2,3-didehydrothiophene (1), followed by a rearrangement of the resulting adduct 11 and dehydrogenation. FVT of 2 in the presence of 2,5- (17b) or 3,4-dimethylthiophene (17c) also gave a mixture of the dimethylthianaphthenes (1822, 23) which can be rationalized as arising by a [4+2]- and two [2+2]-cycloadditions of the aryne 1 to the thiophenes 17 with subsequent desulfurization. The lack of equilibration of the products 18, 22 and 23, was demonstrated and their origin as a function of the structure and reactivity of the aryne 1 discussed.  相似文献   

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