摘要:

7-Acetoxyroyleanone (1a) has been converted in five steps to the methoxy-p-quinone9. Since the latter was the penultimate intermediate in Eugster's partial synthesis of 14-methoxytaxodione (2), the transformation reported represents a formal synthesis of the latter.Keywords: 7-acetoxyroyleanone, 14-methoxytaxodione, synthesis.

ISSN:0008-4042    

DOI:10.1139/v89-001

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

H–D exchange of a series of pyridines1–15, 10H-pyridino[3,2-b][1,4]benzothiazine (16), phenothiazine (17), and aniline has been carried out in neutral D2O at elevated temperatures. The substrates undergo selective exchange and are generally isolated in good yield. Cyanopyridines4,5, and6hydrolyze readily in D2O at elevated temperatures, and the resultant carboxylic acids decarboxylate. This reaction provides a convenient one-step route to selectively labelled pyridines. Possible mechanisms of exchange are presented.Keywords: protium–deuterium exchange, substituted pyridines, temperature effect

ISSN:0008-4042    

DOI:10.1139/v89-002

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The conformational properties of the 3-halogenated-1-benzoxepins (compounds6–9) have been studied by1H and13C dynamic nuclear magnetic resonance. The results show that for the heavier halogen derivatives (Cl, Br, and I), only two chair forms (CaandCe) are observed while for the F substituent, three forms (Ca,Ce, andTB) are detected. This is in contrast with the 3-halogenated-1,5-benzodioxepins (2–5), which were shown to exist as a mixture of three forms for the heavier halogens (Cl, Br, and I) and, show only two forms (CaandTB) for the F substituent. The results for these two systems characterize the conformational effects produced by one and two O—C—C—X vicinal interactions between polar bonds, which shed light on the nature of the intramolecular stereoelectronic σ–σ* orbital interactions operative in both families of molecules.Keywords: 3-halogenated-1-benzoxepins, conformational properties, nuclear magnetic resonance, stereoelectronic orbital interactions

ISSN:0008-4042    

DOI:10.1139/v89-003

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The secondary α-deuterium kinetic isotope effects and substituent effect found in the SN2 reactions between a series ofpara-substituted sodium thiophenoxides and benzyldimethylphenylammonium ion are significantly larger when the reacting nucleophile is a free ion than when it is a solvent-separated ion pair complex. Tighter transition states are found when a poorer nucleophile is used in both the free ion and ion pair reactions. Also, the transition states for all but one substituent are tighter for the reactions with the solvent-separated ion pair complex than with the free ion. Hammett ρ values found by changing the substituent on the nucleophile do not appear to be useful for determining the length of the sulphur–α-carbon bond in the ion pair and free ion transition states.Keywords: Isotope effects, ion pairing, nucleophilic substitution, SN2 reactions, transition states.

ISSN:0008-4042    

DOI:10.1139/v89-004

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The cation mobility μ+was measured in n-pentane at 295 K and inn-C6to C11andn-C14alkanes from ~295 K to their normal boiling points. The dependence on viscositywas reexamined and the best fit occurred withp = 1.0. The ratio of diffusion coefficients of neutral molecules to analogous cations was ~3 because of the stronger interaction of ions with the fluid molecules (electrostriction). The dependence of μ+on free volume is illustrated.Keywords: thermal cation mobility,n-alkane solvents, viscosity effects

ISSN:0008-4042    

DOI:10.1139/v89-005

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The macrocyclic polyether 18-crown-6 forms complexes with hydrates of strong acids derived from transition metal chlorides and hydrochloric acid. The following charged-component complexes have been isolated and characterized: 18-crown-6.H3O+.FeCl4−, 18-crown-6.H3O+.InCl4−, and (18-crown-6.H3O+)2.Pd2Cl62−. X-ray diffraction study of the palladium complex is reported. The oxonium ion is located at the center of the macrocyclic ether cavity and the symmetry of the ring is close toD3d.Keywords: 18-crown-6 complexes, oxonium ions, X-ray diffraction, crystal structure

ISSN:0008-4042    

DOI:10.1139/v89-006

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

6,6-Disubstituted 2,4-cyclohexadien-1-ones can be prepared by dibromination–bisdehydrobromination of the corresponding 6,6-disubstituted 2,2-dibromocyclohexanones. Such dienes undergo Diels–Alder reactions with dimethyl acetylenedicarboxylate to give 3,3-disubstituted 5,6-di(methoxycarbonyl)bicyclo[2.2.2]octa-5,7-dien-2-ones; when the substituents at C-6 in the dienones are different, two diastereomers of the adducts are formed in a ratio dependent on the "facial selectivity" in the Diels–Alder reactions. For the cases where one of the 6-substituents is methyl and the other is methoxycarbonyl, acetoxymethyl, dibromomethyl, or dichloromethyl it has been established via X-ray crystallography and chemical correlation that theendo-3-methyl/exo-3-methyl product ratio is 3.0, 0.9, 8, and 6, respectively. The origin of these differences is discussed briefly and a spectroscopic method for the assignment of structures to the individual diastereomers is proposed.Keywords: Diels–Alderreactions, substituted 2,4-cyclohexadien-1-ones, facial selectivity, dimethyl acetylenedicarboxylate.

ISSN:0008-4042    

DOI:10.1139/v89-007

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

Reaction of "cyclamphosphorane" (cyclamPH) with [Pt2Cl4(PEt3)2] yields [PtCl(PEt3)(cyclamPH)]Cl. The complex crystallizes as a dichloromethane solvate in the monoclinic space group P21/n, witha = 13.877(3),b = 23.231(7),c = 8.295(2)Å, β = 91.86(4)°, and an X-ray diffraction study shows square planar platinum coordination in which the labile proton of cyclamPH has transferred from phosphorus to nitrogen and the ligand is attached via simplechelation. The phosphorus istransto chlorine in the platinum coordination plane.The corresponding product,trans-[PtCl2(PEt3)(cyclenPH2)]Cl, derived from reaction of "cyclenphosphorane" (cyclenPH) with [Pt2Cl4(PEt3)2], is shown by NMR studies to have a quite different structure in which the ligand is protonated at two nitrogen sites but not at phosphorus. The phosphorus is pentacoordinate with four attachments to nitrogen atoms and one to platinum. The two chlorine atoms are mutuallytransin the platinum coordination plane.Keywords: crystal structure, cyclenphosphorane reaction, cyclamphosphorane reaction, X-ray diffraction.

ISSN:0008-4042    

DOI:10.1139/v89-008

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

The orientational order parameters ofortho-,meta-, and para-dichlorobenzene, dissolved in the nematic solvents EBBA and 1132, have been measured as functions of temperature and concentration, and used to determine the values of the potential energy parameters for each solute–solvent pair. These potentials have been interpreted in terms of a short-range contribution, which depends upon the shape and size of the solute molecule, plus a long-range term due to the interaction between the average electric field gradient from the solvent and the molecular quadrupole moment of the solute.Keywords: dichlorobenzenes, nematic solvents, liquid crystals, orientation, potential energy parameters.

ISSN:0008-4042    

DOI:10.1139/v89-009

出版商:NRC Research Press    

年代:1989

数据来源: NRC

摘要:

1-Acenaphthenol was resolved by fractional crystallization of its camphanate ester followed by hydrolysis. The absolute stereochemistry of the (+)-camphanate and (−)-alcohol, derived therefrom, was established as (R) by X-ray crystallography.Keywords: (−)-acenaphthenol, stereochemistry, synthesis, X-ray crystallography.

ISSN:0008-4042    

DOI:10.1139/v89-010

出版商:NRC Research Press    

年代:1989

数据来源: NRC