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1.
(1 S,4 S)-7-Oxabicyclo[2.2.1]hept-5-en-2-one ((−)-5, a “naked sugar”) has been converted to (−)-(1 R,4 S,6 S)-6- endo-benzyloxy-2-bromo-7-oxabicyclo[2.2.1]hept-2-ene ((−)-12) in a highly stereoselective fashion. Double hydroxylation of the C=C double bond of (−)-12, followed by acetylation and Baeyer-Villiger oxidation of the resulting -acetoxyketone (−)-14 afforded (−)-5-O-acetyl-2-O-benzyl-3-deoxy-β-D- arabino-hexofuranurono-6,1-lactone ((−)-15). This compound was converted readily into (+)-methyl 3-deoxy--D- arabino-hexofuranoside ((+)-6 and (+)-methyl 3-deoxy-β-L- xylo-hexofuranoside ((+)-7) and partially protected derivatives. (−)-15 was also converted into 4-deoxy-D- lyxo-hexopyranose (34) and several partially protected derivatives such as (+)-methyl 4-deoxy-2,3-O-isopropylidene--D- lyxo-hexopyranoside ((+)-8). 相似文献
2.
Asymmetric hydroboration of [ E]- and [ Z]-2-methoxy-2-butene, using (−)-diisopinocampheylborane at −25°C in THF solvent, followed by oxidation using H 2O 2/NaOH, gave (−)-[2 R,3 R]- and (+)-[2 R,3 S]-3-methoxy-2-butanols in >97 and 90% ee, respectively. (−)-[2 R,3 R]-3-Methoxy-2-butanol was converted to (−)-[2 R,3 R]-butane-2,3-diol (>97% ee, in an overall yield of 65%). 相似文献
3.
(+)- and (−)-etodolac enantiomers were prepared both by classical resolution via crystallisation of diastereoisomeric salts with (+) and (−)--methylbenzylamine, and by suitable manipulation of derivatives (−)-3- and (+)-4, obtained by lipase-catalysed kinetic resolution of racemic 3 X-ray diffraction analysis of the 4-bromobenzoate derivative of (+)-3, obtained from enantiopure acetate (+)-4, allowed us to determine the absolute (R) configuration of (−)-etodolac. 相似文献
4.
Acid-catalyzed condensation of (+)-mollisacacidin-[(2 R, 3 S, 4 R)-2, 3-trans-3, 4- trans-flavan-3,3′,4,4′,7-pentaol] with an excess of (−)-robinetinidol[(2 R,3 S)-2,3-trans-flavan-3,3′,4′,5′,7-pentaol] afforded a novel series of bi-, tri-, and tetraflavanoid profisetinidins. They are accompanied by (−)-fisetinidol-(4,2′)-(−)-robinetinidol which results from the pyrogallol B-ring of (−)-robinetinidol serving as nucleophile competing with its resorcinol A-ring in coupling with a C-4 carbocationic intermediate. Similar condensation with (+)-epifisetinidol[(2S,3S)-2,3-cis-flavan-3,3′,4′,7-tetraol] led to the exclusive formation of [4,6]-interflavanyl bonds, these units being ‘linearly’ arranged in the tetraflavanoid analogue in contrast to the ‘branched’ nature of the (−)-robinetinidol homologue. 相似文献
5.
Attempted enantioselective deprotonation of fluorobenzenetricarbonylchromium(0) with ca. 1 equivalent of butyllithium/(−)-sparteine in ether–hexane at −78°C followed by a chlorotrimethylsilane quench gave the racemic ortho-substituted product. Analogous enantioselective deprotonation of anisoletricarbonylchromium(0), followed by electrophilic quench, gave the 1-( Rp)-substituted complexes in up to 77% yield with 27% e.e., but with methoxymethoxybenzenetricarbonylchromium(0), (4-triisopropylsilyloxymethyl)methoxymethoxybenzenetricarbonylchromium(0) and ( N- t-butoxycarbonylaniline)tricarbonylchromium(0), the 1-( Sp)-products were formed in up to 58% yield with 92% e.e. The results are explained in terms of coordinative and non-coordinative enantioselective lithiation. 相似文献
6.
Optically active o-substituted diphenyl N-substituted sulphilimines are readily synthesised by the reaction of the corresponding sulphides and t-butyl hypochlorite in the presence of l-menthol and amide anions. (−)-N- p-Tolylsulphonylsulphilimines (1, 2) obtained were converted to the corresponding (−)-N-unsubstituted sulphilimines (8, 9) by treating them with concentrated sulphuric acid. When (−)-S- o-anisyl S-phenyl N-(unsubstituted) sulphilimine (8) was treated with acylating agents or acrylonitrile, the corresponding optically active (−)-N-substituted sulphilimines were prepared with complete retention at sulphur. The absolute configuration of (−)-S- o-anisyl S-phenyl N- p-tolylsulphonylsulphilimine (1) was determined by converting it to (+)-S- o-anisyl sulphoxide (17). CD curves of (−)- o-substituted diarylsulphilimines exhibited a negative Cotton effect at around 270–285 nm, which was assigned to ( S)-configuration at sulphur by comparing with the analogous sulphoxides. The substituent on the imino group of the sulphilimine gave no appreciable effect on the CD behavior and the lack of substituent effect was considered to be due to the semi-polar character of the S(IV)-N bond. Unusual effect of o-methoxy group on the CD curves was discussed in connection with solvent effect. Mechanism of this asymmetric synthesis has been investigated, and it has become apparent that the diastereomeric menthoxysulphonium chloride was an excess of ( RR)-configuration was formed initially and the amide anion attacks the S atom of the salt with net inversion. 相似文献
7.
(−)-Tabersonine 4 was submitted to quaternization and Emde degradation to yield the 3,4- seco derivative 5, which was hydrolyzed and decarboxylated to the diastereomeric indolenines 8 and 9. Oxidative rearrangement of 8 and 9 yielded the two diastereomeric seco-rhazinilams (−)-10 and (+)-11, differing in the atropomeric conformations of their biarylic system. The results are discussed in the realm of oxidation and rearrangements in the aspidosperma series of indole alkaloids. 相似文献
8.
A new lead(II) electrode has been constructed with poly(hydroxamic acid) (PHXA) as the active material and silicone rubber as the supporting material. The electrode gave near Nerstian response over the concentration range 4 × 10 −5−1 × 10 −2M lead(II). The detection limit of the electrode is approximately 4 × 10 −6M and the electrode works well in the pH range 4.5–6.0. The response time was 50–120 sec over the whole concentration range and the electrode has a working life of at least 4 weeks. Iron(III) severely poisoned the electrode membrane. Nickel(II) and mercury(II) gave very strong interference compared to copper(II), silver(I), cobalt(II), sodium(I), potassium(I), zinc(II) and cadmium(II) which gave some or little interference. Values determined with atomic absorption (AAS) and a commercial lead(II) electrode were in good agreement with those measured with the lead(II) electrode reported here. 相似文献
9.
The photochemistry of a variety of dicyanopyridines (2,3-, 2,4-, 2,5-, 2,6-, 3,4- and 3,5-dicyanopyridine) in solution at room temperature was investigated. Pulsed UV (308 nm) laser irradiation in deoxygenated acetonitrile yields the triplet state with lifetimes between 4 and 10 μs and absorption bands in the 400 and 320 nm regions. In the presence of added HCl an air-insensitive transient (τ ≈ 10–12 μs, λ max ≈ 360–380 nm) was observed, suggesting the formation of a protonated excited state. Irradiation in the presence of amines resulted in the production of the pyridyl radical anion (τ ≈ 40–80 μs, air sensitive, λmax ≈ 360–380 nm) formed by electron transfer from the amine to the pyridine triplet excited state. Stern-Volmer analysis gave electron transfer rate constants in the range (1–8) × 10−8 M−1 s−1. In methanol solvent, irradiation yielded an air-insensitive transient assigned as the neutral pyridyl radical (τ ≈ 30–200 μs, λmax ≈ 370–385 nm). The formation of these transients is discussed in the context of previous photochemical electron spin resonance and product studies. 相似文献
10.
The “naked sugar” (+)-(1 R, 4 R)-7-oxabicyclo[2.2.1]hept-5-en-one((+)-2) has been converted to D-lividosamine ((+)-1: 3-deoxy-D-glucosamine) and derivatives via (+)-2-chloro-2,3-dideoxy-5,6-O-isopropylidene-D- arabino-hexono-1,4-lactone ((+)-33) and (+)-2-azido-2,3-dideoxy-5,6-O-isopropylidene-D- ribo-hexono-1,4-lactone ((+)-34) in a highly stereoselective fashion. Similarly, 2-acetamido-2,3-dideoxy-D- arabino-hexose and derivatives were derived from the “naked sugar” (−)-(1 S,4 S-7-oxabicyclo[2.2.1]-hept-5-en-2-one ((−)-2) via the double hydroxylation of the C=C double bond in (−)-N-benzyl-N-[(1 R,2 S,4 S)-6-bromo-7-oxabicyclo[2.2.1]hept-5-en-2-endo-yl] amine ((−)-40). 相似文献
11.
The seeds of Millettia dura (Dunn) have yielded durlettone, durmillone, mildurone, (−)-millettone, (−)-millettosin, (−)-rotenone, (−)-tephrosin, (−)-tephrosin, and 6 ω12 ω-dehydrodeguelin. The constitutions of the new isoflavones durlettone (I), durmillone (IV), and milldurone (VIII) have been established. Millettone is shown to be the new rotenoid (XIX). The natural co-occurrence of the rotenoids, (−)-millettone (XIX) and (−)-rotenone (XX), with the 12a-hydroxyrotenoids, (−)-millettosin (XXI) and (−)-tephrosin (XXII), and the 6a,121-dehydrorotenoid, 6a,12a-dehydrodeguelin (XII), is established. The relation of these observations to the question of the natural occurrence of 12a-hydroxyrotenoids and 6a,12a-dehydrorotenoids is discussed. 相似文献
12.
The enantioselective synthesis of (−)-lasubine I 1 and the first asymmetric synthesis of (−)-lasubine II 2 and (+)-subcosine II 3 is described. The key step is the intramolecular cyclization of N-acyliminium ion 4 which is derived from ( S)-aminoester 6. 相似文献
13.
A study has been made of asymmetric hydroformylation of styrene with PtCl 2(PPh 3) 2 + bisphosphine + SnCl 2 (bisphosphine: BDPP = (−)-(2 S,4 S)-2,4-bis(diphenylphosphino)pentane or DIOP = (−)-(4 R,5 R)-2,2-dimethyl-4,5-bis(diphenylphosphinomethyl)-1,3-dioxolane) and PtCl 2(bisphosphine) + PPh 3 + SnCl 2 catalysts prepared “in situ”. The presence of an excess of the phosphine ligand slightly lowered the reaction rate, but the enantioselectivity of these systems is significantly higher than those involving PtCl(SnCl 3)(bisphosphine) catalysts. Under mild reaction conditions 88.8% enantiomeric excess was achieved. Replacing SnCl 2 in these catalysts by CuCl 2 or CuCl gave a new homogeneous catalytic system which is active at higher reaction temperature (> 100°C), but has a rather moderate enantioselectivity. 相似文献
14.
Starting from 8-bromoadenosine, 2′,3′-O-isopropylidene-(IIa) and 2′,3′-O-ethoxymethylidene-5′-O-tosyl-8-bromoadenosme (IIb) were synthesized. Compounds IIa, b gave 8,5′-anhydronucleosides (IV a and b) on treatment with hydrogen sulfide in pyridine or aqueous sodium hydrogen sulfide in pyridine at −5–−15°. The structure of IV was confirmed by UV absorption, NMR and elemental analysis. CD and ORD measurements of IV showed large positive Cotton effects around absorption maxima. Acidic removal of the protecting group in IV gave 8,5′-anhydro-8-mercaptoadenosine (V), which was desulfurized to afford 5′-deoxyadesine (VI). 相似文献
15.
The stoichiometry of thermal decomposition has been studied for (I): [Ni(4-EtPy) 4(NCS) 2] as a host complex as well as for its clathrates [Ni(4-EtPy) 4(NCS) 2]· G where guest molecule G - toluene, (II): T, (III): o-xylene ( o-X) and (IV): p-xylene ( p-X). The loss of volatile components proceeds in three steps (−2 L, −1 L, −1 L) for I and in four steps (− G, −2 L, −1 L, −1 L) for II, III and IV. DSC and X-ray powder measurements indicated a phase transition in all compounds under study. However, this process is overlapped by the escape of G in II and III. The differences in enthalpy changes are associated with different guest-host interactions in the particular clathrates. 相似文献
16.
Racemic 1,1′-methylene[(1 RS,1′ RS,3 RS,3′ RS,5 RS,5′ RS)-8-oxabicyclo[3.2.1]oct-6-en-3-ol] ((±)-6) derived from 2,2′-methylenedifuran has been resolved kinetically with Candida cyclindracea lipase-catalysed transesterification giving 1,1′-methylenedi[(1 R,1′ R,3 R,3′ R,5 R,5′ R)-8-oxabicyclo[3.2.1]oct-6-en-3-ol] (−)-6 (30% yield, 98% ee) and 1,1′-methylenedi[(1 S,1′ S,3 S,3′ S,5 S,5′ S)-8-oxabicyclo[3.2.1]oct-6-en-3-yl] diacetate (+)-8, (40% yield, 98% ee). These compounds have been converted into 1,1′-methylenedi[(4 S,4′ S,6 S,6′ S)- and (4 R,4′ R,6 R,6′ R)-cyclohept-1-en-4,6-diyl] derivatives. 相似文献
17.
Enantioselective acetylation of (±)-4-(1-hydroxyethyl)benzenesulfonamide 6 with ‘Acylase I’ (No. A 2156) from Aspergillus melleus in the presence of vinyl acetate gave ( R)-4-(1-acetoxyethyl)benzenesulfonamide 7 (98% ee) and ( S)-6 (98% ee). Both ( S)-6 and ( R)-7 were individually converted to the ( S)-hydroxyhexamide 2 (>99% ee) and ( R)-hydroxyhexamide 2 (>99% ee), respectively. The absolute configuration of a metabolite (−)-hydroxyhexamide 2 from acetohexamide 1 was found to be S based on unequivocal chemical methods including X-ray analysis. 相似文献
18.
Neomethymycin (I) has been transformed into “anhydro cycloneomethynolide” (V) which could be degraded via (−)--methyllevulinic acid to (−)--methylsuccinic acid, thus establishing the absolute configuration of positions 4 and 6 in the lactonic acid (XIII). This acid is a common degradation product of methymycin, neomethymycin, pikromycin and narbomycin and there is thus available a standard of absolute configuration for these macrolide antibiotics. By a different sequence of reactions, erythromycin (XXIII) has been converted into (+)--methyllevulinic acid and (+)--methylsuccinic acid. Coupled with earlier results reported in the literature, it is now possible to assign absolute configurations to positions 10 (R) and 8 (R) of erythromycin and this applies most likely also to positions 4 (R) and 2 (S). Attention is called to the biogenetic significance of these observations. 相似文献
19.
1-Pentene has been polymerized in the presence of deuterium using as catalyst precursors [Al(CH 3)-O] n and (−)-ethylenebis(4,5,6,7-tetrahydro)-( R)-1-indenylzirconium derivatives ((−)-( R)-EBTHI-ZrX 2, X = CH 3 (I); X = ( R)-1′,1″-bi-2-naphtholate (II)). The investigation of 1,2-dideuteriopentane and of the deuteriooligomers thus obtained shows that the ( Re) enantioface of the olefin is predominantly involved in the deuteration but its ( Si) enantioface in the dimerization and oligomerization. These results, which show the participation of the growing chain in the enantioface discrimination in the stereospecific polymerization of 1-pentene are discussed on the basis of a simple stereochemical model for the transition state of the olefin insertion step. 相似文献
20.
The natural hydroxyamides, (−)-tembamide and (−)-aegeline, and the cardiac drug (−) -denopamine have been prepared in homochiral form in good overall yield (>65%) from para - methoxy or para-allyloxybenzaldehyde by synthetic sequences involving entantioselective hydrocyanation of the aldehydes. Similar chemistry has been used to prepare analogues of the bronchodilator (−)-salbutamol both in high yield and with good enantiomeric excess. 相似文献
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