摘要:

The development of organometallic-type reactions in aqueous media is reviewed. Coupling reactions of allyl halides with carbonyl compounds mediated by zinc, or tin, or indium in aqueous media to give homoallylic alcohols are discussed. The stereochemical outcome is compared with similar reactions in organic solvents. A concise synthesis of (+)-muscarine is used to illustrate the usefulness of aqueous organometallic-type reactions in organic synthesis. The procedure to protect–deprotect hydroxy functional groups may not be necessary in these reactions. An application in the carbohydrate area is demonstrated with the synthesis of (+)-3-deoxy-D-glycero-D-galacto-nonulosonic acid (KDN). The mechanistic possibilities of organometallic-type reactions in aqueous media are outlined.

ISSN:0008-4042    

DOI:10.1139/v94-151

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The stereofacially differentiated enone ester5has been used to study the effects of steric influence on the Diels–Alder reaction. In general, under Lewis acid catalysis,5adds to dienes at low to ambient temperatures in a reasonable rate. Yields of predictable chiral adducts are moderate with the unexpected exception of zinc chloride catalyzed reactions, which provide good to high yields. In all cases only products of addition to theSiface of general type21were observed. The regiochemistry of the adducts is exclusively that predicted by theorthoandpararules. The stereochemistry shows a high selectivity in favor ofester-endotransition state products. Rationales for the observed stereoselectivities are discussed. The fragmentation of adducts of5, in particular keto ester9, has been briefly examined. Olefins30and46derived from9have been converted to ring-opened cadinane skeletons31and47, respectively, by conditions we have previously reported. In an entirely new and unexpected reaction, simultaneous ketalization and fragmentation of the cyclobutane ring of ketones derived from9gave ring-opened ketals34 + 35(from29),36 + 37(from9),39(from38) and42 + 43(from40).

ISSN:0008-4042    

DOI:10.1139/v94-152

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Polarized near-infrared spectra of single crystals of CsMnCl3•2X2O (X = H, D) were recorded at 10 K. Those bands which could be assigned to O—H or O—D stretch overtones were analyzed using local-mode theory specifically adapted for systems having less thanC2vsymmetry. Both O—H oscillators form nearly linear hydrogen bonds to neighboring chloride ions at different distances. As a result, the local-mode harmonic frequency and anharmonicity parameters show characteristic shifts from their gas-phase values. The parameter values cover an unusually narrow range in this crystal, considering the spread in hydrogen-bond distances. Assignment of stretch overtone bands to specific oscillators in the crystal was made by using the polarization behavior expected of local modes in the oriented gas model. Several of the overtone bands show combinations with lattice modes or low-energy hydrogen-bond modes in unusual detail.

ISSN:0008-4042    

DOI:10.1139/v94-153

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Solid phase 45.3 MHz13C NMR spectra ofortho-dimethoxydiphenyl ether,1, dibenzo[b,e]-15-crown-5- ether,2, and tetrabenzo[b,e,q,t]-30-crown-10 ether,3, have been obtained. Chemical shift trends are discussed in terms of the asymmetric units and structural features available from X-ray crystallographic data. Comparison with solution13C spectra are made. The crystal structures of1and3were determined by X-ray diffraction at room temperature.1crystallizes in space groupP21/awitha = 13.366(1),b = 8.230(1),c = 12.303(1) Å, β = 116.63(1)°,Z = 4.3crystallizes in space groupP21/cwitha = 7.903(1),b = 26.337(2),c = 7.852(1) Å, β = 97.28(1)°,Z = 2. The structures were solved by direct methods and refined by full-matrix least squares to residuals of 0.055 using 1727 reflections for1and of 0.042 using 2590 reflections for3.

ISSN:0008-4042    

DOI:10.1139/v94-154

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Complexes of the type [Pt(L)X] where L is a tridentate N ligand and X = Cl or I, were synthesized and characterized. Three of the ligands are N-derivatives of diethylenetriamine, (2-aminoethyl)(N-dimethyl-2-aminoethyl)amine, (2-aminoethyl)(N-diethyl-2-aminoethyl)amine, and (2-aminoethyl)(N-methyl-2-aminoethyl)N-methylamine. The other two ligands are di(3-amino-propyl)amine and (2-aminoethyl)(3-aminopropyl)amine. A new method for the synthesis of the chloro complexes from the direct reaction of the amine with K2[PtCl4] was developed. The reactions of these five compounds with several purine and pyrimidine bases were studied by NMR techniques. The Pt(II) complexes containing two five-membered chelates were shown to be more reactive than the one containing two six-membered rings, while the complex containing one five- and one six-membered chelates showed intermediate reactivity. For the diethylenetriamine derivatives, the complexes containing ligands with two alkyl groups on the same terminal N atom were more reactive than the one containing one methyl group on a terminal N atom and one methyl group on a non-terminal N atom.

ISSN:0008-4042    

DOI:10.1139/v94-155

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The Generalized-Valence-Bond-Perfect-Pairing (GVB-PP) method has been used to investigate the structural behaviour, energy, and dipole moment along the reaction coordinates for propene ↔ H + cis- ortrans-propen-1-yl. Geometry optimizations were carried out at the GVB(9)/STO-3G level (complete valence shell) for the minimum energy propene structure (complete optimization) and for numerous structures up tor(C—H) = 10 Å (only the elongated C—H distance kept fixed). The dissociation curves are smooth, without a maximum, and yield predicted dissociation energies of propene to H + cis-propen-1-yl and H + trans-propen-1-yl of 555.8 and 554.8 kJ mol−1, respectively. These values are within several percent of those obtained for C—H bond rupture in ethylene using GVB and MCSCF methods with the same basis set. They are obviously too high but they confirm that removal of a hydrogen atom from the CH2moiety in propene requires about the same energy as removal of a hydrogen atom from ethylene. GVB(7)/6-31G//GVB(9)/STO-3G computations lower the predicted dissociation energies of propene ↔ H + cis-propen-1-yl and H + trans-propen-1-yl to 448.2 and 448.6 kJ mol−1, respectively.The reduced energy concept (ER = (E∞ − Er)/De) is applied to the reaction coordinates. Linear behaviour for InERversus bond length is observed at long bond distances. Atr(C—H) = 3 Å, the values of the slopes, d(lnER)/dr(C—H), which are related to the effective Morse constantBare −3.73 and −3.74 (GVB(9)/STO-3G) and −2.75 and −2.81 (GVB(7)/6-31 G//GVB(9)/STO-3G) for the H +cis- and H +tras-propen-1-yl reaction coordinates, respectiv

ISSN:0008-4042    

DOI:10.1139/v94-156

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Four commercially available metallothioneins from rabbit liver (RL, RL I, RL II) and from horse kidney (HK) have been studied by size exclusion chromatography and by reverse-phase chromatography, to characterize their polymorphism. The isoforms are detected by UV at 250 nm. Separations by size exclusion show that the metallothioneins are partially dimerized, with molar rates of dimer ranging from 5% for HK to 15% for RL II. The four chromatograms obtained by reverse phase exhibit a different morphology: RL separates in four main isoforms, RL I into two, RL II into three, and HK into two. An attribution of the various peaks for the RL, RL I, and RL II series is proposed. The comparable results obtained by the two methods allow us to estimate that RL is composed of 20–30% RL I and 70–80% of RL II.

ISSN:0008-4042    

DOI:10.1139/v94-157

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

Three types of potential photoionophores based on polycarboxylic acid crown ethers were prepared, and their cation complexation behaviours and spectroscopic properties were surveyed. The first type were neutral macropolycyclic hosts prepared by capping across the faces of the crown ether with aromatic diamine chromophores. The second were bis-crown ether carboxylates bearing a bridging aromatic chromophore. The third type appended an additional chromophore-donor site on the crown ether carboxylic acid framework. Cation complexation was examined by potentiometric titration. The neutral ligands were rather poor hosts for alkali metal cations. The other two types of crown ether carboxylates showed a combination of size selectivity and electrostatic stabilization, leading to significant and selective ion binding in water. Ligands of the third type also exhibited cation-dependent absorption spectra in neutral and basic aqueous solution. No significant alkali metal or alkaline earth cation-induced perturbation of the emission spectra was uncovered, but a sodium- and cesium-dependent long wavelength emission enhancement was observed in one of the neutral ligand systems.

ISSN:0008-4042    

DOI:10.1139/v94-158

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

The photochemistry in methanol of 1-naphthylmethyl phenyl carbonate (3) and 1-naphthylmethyl benzyl carbonate (4) has been studied. Products resulting from both the 1-naphthylmethyl cation and the 1-naphthylmethyl radical are obtained for3, but only from the cation for4. Similar results were obtained for the corresponding 1-naphthylmethyl derivatives5and6ofN-phenyl andN-benzyl carbamic acids. The product yields for all four compounds can be explained by a mechanism of initial homolytic cleavage of the 1-naphthylmethyl carbon–oxygen bond from the excited singlet state. The radical pair generated then partitions between the two pathways: electron transfer to form the ion pair or decarboxylation. For PhO-CO-O•and PhNH-CO-O•, decarboxylation is rapid and competitive with electron transfer. For PhCH2O-CO-O•and PhCH2NH-CO-O•, decarboxylation is slower, electron transfer dominates, and only products from the ion pair are obtained.

ISSN:0008-4042    

DOI:10.1139/v94-159

出版商:NRC Research Press    

年代:1994

数据来源: NRC

摘要:

TheC-aryl glucals17–31have been prepared by the palladium-catalyzed cross coupling of 1-tributylstannyl-3,4,6-tri-O-(tert-butyldimethylsilyl)-D-glucal (11) and aryl bromides. The major by-product in all of these reactions is the dimer33, the product of homocoupling of11. Alternatively, theC-aryl glucals34–40can be obtained from the palladium-catalyzed coupling of 1-iodo-3,4,6-tri-O-(triisopropylsilyl)-D-glucal (16) and a variety of metalated aromatics, including ArZnCl, ArB(OH)2, and ArB(OMe)2. The advantages of the latter procedure include superior coupling yields under milder reaction conditions and the high yielding preparation of16directly from 3,4,6-tri-O-(triisopropylsilyl)-D-glucal (12) by a metalation–iodination sequence.

ISSN:0008-4042    

DOI:10.1139/v94-160

出版商:NRC Research Press    

年代:1994

数据来源: NRC