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1.
Development of successively higher field nmr spectrometers has facilitated the study of increasingly more complex molecules, although smaller molecules such as phenanthro[3,4-b]thiophene still offer very substantial assignment problems because of the highly congested nature of their 1H- and 13C-nmr spectra. Assignments of such spectra, if they are to be unequivocal, frequently require the utilization of two-dimensional nmr spectroscopic techniques. Total assignments of the 1H- and 13C-nmr spectra of phenanthro[3,4-b]thiophene are reported. Assignments were based on a conventional high resolution 500 MHz 1H-nmr spectrum, autocorrelated two-dimensional 1H-nmr spectra (COSY), two-dimensional 1H-13C chemical shift correlation spectra and a modified version of autocorrelated 13C-13C double quantum coherence two-dimensional nmr spectroscopy. From NOE measurements, a separation of 1.99 Å between H1 and H11 was computed, suggesting that phenanthro[3,4-b]thiophene has a pronounced helical conformation in solution.  相似文献   
2.
The separation of diastereomeric esters derived from (±)-pyridylethanols and 3β-acetoxyetienic acid were achieved by an extraction technique using diethyl ether and aqueous hydrochloric acid. A formal total synthesis of PNU-142721 was effectively carried out to prepare the chiral, non-racemic synthon 1-furo[2,3-c]pyridin-5-yl-ethanol (1) by means of this technique. The structure optimized using MOPAC calculations on each diastereomer suggested the presence of intramolecular CH/π interaction in only the (S)-isomer of the diastereomers.  相似文献   
3.
A highly efficient route to 3,4-diarylpyrrole marine alkaloids has been developed using Hinsberg-type pyrrole synthesis and palladium-catalyzed Suzuki cross-coupling of the 3,4-dihydroxypyrrole bis-triflate derivatives as key reactions. Based on this approach, formal syntheses of permethyl storniamide A and ningalin B, and a total synthesis of lamellarin G trimethyl ether have been achieved.  相似文献   
4.
Generation of singlet and triplet 2-silylcyclopentane-1,3-diyls and their reactivity have been investigated in the thermal and photochemical denitrogenation of 2,3-diaza-7-silylbicyclo[2.2.1]hept-2-ene. 5-Silylcyclopentene (silyl migration product) is quantitatively obtained, while 5-silylbicyclo[2.1.0]pentane (intramolecular ring-closure product) is not detected in the denitrogenation reactions. Deuterium labeling studies clarify that 5-silylcyclopentene is formed by a suprafacial [1,2] silyl migration in singlet 2-silylcyclopentane-1,3-diyl. UDFT calculations closely reproduce the observed reactivity of the singlet diradical: The enthalpic barriers of the intramolecular ring-closure are calculated to be DeltaH++exo468 = 5.8 kcal/mol and DeltaH++endo468 = 6.7 kcal/mol, which are much higher than the energy barrier for the [1,2] silyl migration, DeltaH++468 = 2.7 kcal/mol. The notable effect of the silyl group on raising the energy barrier of the intramolecular cyclization is rationalized by an electronic configuration of the lowest singlet state of 2-silylcyclopentane-1,3-diyls.  相似文献   
5.
Inorganic and organic mercury at ng l?1 levels in fresh waters are collected simultaneously on a column of a dithiocarbamate-treated resin and quantitatively eluted with slightly acidic aqueous thiourea solution. Mercury vapor is generated from inorganic mercury by reduction with alkaline SnCl2 solution, and from inorganic and organic mercury with a CdCl2SnCl2 solution, for determination by cold-vapor atomic absorption spectrometry. The range of determination is 0.2–5,000 ppt (ng l?1) for 20-l water samples.  相似文献   
6.
Treatment of N-heteroarylacethydrazides with an equimolar amount of nitrous acid afforded N-heteroaryacetylazides and subsequent thermolysis of these azides gave the analogues of 2,3-dihydroimidazo[1,5-a]pyridin-3-one. When some of these cyclized compounds were treated with nitrous acid, the ring opening reaction occurred and recyclized 3-(N-heteroaryl)-1,2,4-oxadiazolin-5-ones were obtained. Treatment of N-heteroarylacethydrazides with two equivalent moles of nitrous acid afforded α-oximino-α-(N-heteroaryl)acetylazides. Thermolysis of these azides gave mixtures of 3-(N-heteroaryl)-1,2,4-oxadiazolin-5-one and 3-hydroxy-4-(N-heteroaryl)furazan. On the basis of the effects of heterocyclic rings and solvents upon the relative yield of two types of the products, one plausible mechanistic explanation for the decomposition of such azides was proposed. α-Oximino-α-(H-heteroaryl)acetylazides were converted into cyano N-heterocycles by the action of alkali in good yields.  相似文献   
7.
A method was investigated in which all of the phthalate esters in biological samples were determined as phthalic acid by gas-liquid chromatography. The method is based on the separation of phthalate esters from the sample with n-hexane, saponification of the esters with an alkaline ethanolic solution to give phthalic acid, purification of the acid by extraction with diethyl ether and column chromatography using silica gel, and conversion of the acid into bis(2,2,2-trifluoroethyl) phthalate with a 2,2,2-trifluoroethanol solution containing boron trifluoride. The derivative obtained is highly sensitive to an electron-capture detector, giving a sensitivity of 0.1 pg. Biological samples fortified with di(2-ethylhexyl) phthalate at levels of 5-100 ppb were analyzed, with recoveries of 70-100%.  相似文献   
8.
Photodenitrogenation of the diazenes 4 affords exclusively the housanes 5 through intramolecular cyclization of the spectrally detected and characterized singlet diradicals 3. The lifetime of singlet diradical 3, determined by transient absorption measurements, depends on the Y and Z substituents at the para position of the phenyl ring and has the following order: Y, Z = OMe, OMe > OMe, CN > CN, CN > OMe, H > Cl, Cl approximately CN, H approximately Me, Me > H, H. This unprecedented substituent effect reveals stabilization of the singlet 2,2-dimethoxycyclopentane-1,3-diyl diradicals 3 through radical, zwitterionic, pi-bonding, and hyperconjugative structures.  相似文献   
9.
Methyl and ethyl 2-quinolylacetate were prepared from quinoline 1-oxide via acetoacetie ester derivatives. Methyl 2-quinolyl, 1-isoquinolyl, 6-methoxy-3-pyridazinyl, 4-pyridyl and 2-methyl-4-pyridylacetate were synthesized from the corresponding heterocyclic N-oxides via β-aminoerotonie ester derivatives.  相似文献   
10.
2,3-Dihydroimidazo[1,5-α]pyridin-3-one (IV) was obtained by thermolysis of 2-pyridylacetyl azide (II) which was prepared from 2-pyridylacetohydrazide (I) on treatment with an equivalent mole of nitrous acid. Treatment of I with excess nitrous acid yielded α-oximino-α:-(2-pyridyl)-acetylazide (V). Thermal decomposition of V gave 3-(2-pyridyl)-1,2,4-4H-oxadiazolin-5-one (VII). 2-Cyanopyridine (IX) was obtained from V by the action of alkali. 2,3-Dihydroimidazo-[1,5-α ]pyridin-3-one (IV) was rearranged to VII upon treatment with nitrous acid. J. Chem. Soc., 14, 993 (1977)  相似文献   
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