摘要:

A synthetic strategy towards tricholomic acid and acivicin has been established using the aldol condensation ofN-pyruvilideneglycinatoaquocopper(II) and an optically active aldehyde derived fromS-malic acid as the key bond-forming reaction. Although a viable strategy was developed, no asymmetric induction was observed.

ISSN:0008-4042    

DOI:10.1139/v87-031

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

The13C and1H spectra of aspidocarpine and the spectra, structure, and stereochemistry of the product of its von Braun reaction with cyanogen bromide have been totally assigned by a combination of homonuclear (COSY-45) and direct and indirect heteronuclear shift-correlated 2D nmr spectra.

ISSN:0008-4042    

DOI:10.1139/v87-032

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A systematic comparative study of the conformational dynamics of lupinine and epilupinine, two 1-hydroxymethyl quinolizidine epimers, as a function of phase transition and of their protonation is presented. Lupinine and epilupinine have atrans-quinolizidine configuration and they differ only in the position of the CH2OH group. The axial position of this group allows the formation of an intramolecular hydrogen bond OH … N in lupinine, in contrast to epilupinine in which this group is in the equatorial position. Intrinsic conformational equilibria for both epimers have been defined. Despite the significant difference in the population of the preferred rotamers of lupinine and epilupinine, both epimers adopt very similar crystal structures, but in all other states and forms, e.g., pure liquids, solutions in inert and polar solvents, and protonated salts, they behave in drastically different ways.

ISSN:0008-4042    

DOI:10.1139/v87-033

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

A novel application of13C nuclear magnetic resonance provided the effects of solvent polarity and hydrogen-bond formation on the conformational equilibria for a range of 2-substituted tetrahydropyrans and the results are interpreted in terms of how solvent affects the competition between theendo- andexo-anomeric effects in determining the magnitude of the anomeric effect. In accord with the generally accepted origin of theendo- andexo-anomeric effects (anti-periplanarn–σ* interaction of the oxygen lone-pair orbital with the antibonding orbital of the adjacent C—O bond), theexo-anomeric effect for the α anomer is expected to be weaker because charge delocalization from the glycosidic oxygen to anomeric center is in competition with delocalization from the ring-oxygen atom. The effects of solvent on the relative magnitudes of theendo- andexo-anomeric effects are then considered to arise from the formation of specific complexes with the solvent, and theexo-anomeric effect of a β-glycoside is more strongly influenced. It is contended that hydrogen bonding of solvent to the ring oxygen increases theexo-anomeric effects. For this reason water is particularly effective for the strengthening of theexo-anomeric effect and, thereby, the conformational rigidity of glycosides. Experimental evidence is presented that indicates that the anomeric hydroxyl groups of free sugars dissolved in water tend to prefer the equatorial orientation because these provide stronger hydrogen bonds as proton donors to water.

ISSN:0008-4042    

DOI:10.1139/v87-034

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

It has been found that, contrary to the published report, there is no noticeable reaction between phenol and methyl acrylate in the presence of aluminum chloride to produce phenyl acrylate (1) and dihydrocoumarin (2). Although products having the reported spectral data can be obtained by the reaction of phenol with acrylyl chloride, these products are actually phenyl acrylate and phenyl 3-chloropropionate (4), there being detected no dihydrocoumarin. This reaction has now been extended to several substituted phenols and some naphthols. Attempts at cyclization of phenyl acrylate, phenyl 3-chloropropionate, or their mixtures have been unsuccessful.

ISSN:0008-4042    

DOI:10.1139/v87-035

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

(2S,3R)- and (2S,3S)-[1-14C,3-3H] phenylalanine were fed in separate experiments toDaturainnoxiaplants. The distribution of isotopes in the resultant labeled hyoscyamine and scopolamine indicates that the biosynthesis of the acid moiety of these ester alkaloids, namely (S)-tropic acid, involves the migration of the carboxyl group of phenylalanine to its prochiral C-3 position with retention of configuration.

ISSN:0008-4042    

DOI:10.1139/v87-036

出版商:NRC Research Press    

年代:1987

数据来源: NRC

摘要:

Barbier–Grignard reaction of 3- and 17-steroidal ketones gave excellent yields of the allyl steroids1 + 2and15. These were transformed into a mixture of 1,3- and 1,4-diols by hydroboration–oxidation. The diols3,5, and18were used for the preparation of spirolactones and spiroethers. Thus, the Barbier–Grignard allylation–hydroboration–cyclization sequence proved to be an effective method for the spiroannelation of steroidal ketones. It was also shown that an earlier assignment of the stereochemistry of the diols3and5was erroneous.

ISSN:0008-4042    

DOI:10.1139/v87-037

出版商:NRC Research Press    

年代:1987

数据来源: NRC