Chiroptical properties of 4-substituted flavans

The negative n→π*-band CD of (+)-flavanone (1) proves its absolute configuration to be (2R). The CD of 4-substituted flavans (cis- and trans-) is best explained by assuming a sofa conformation for the dihydropyran ring (C-2 out of plane). For these compounds second-sphere contributions are smaller than third-sphere contributions of the 4-substituent.     

Structure of 16α,17α-(Acetylepimino)pregnenolone 3-acetate in the crystal and in solution

Conclusions The structure of 16,17-(acetylepimino)pregnenolone 3-acetate in the crystal and in solution has been investigated. The conformation of the 17-acetyl group scarcely changes on passing from the crystalline state into solution.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 5, pp. 1110–1116, May, 1986.     

Oxazepines and thiazepines,XXVIII Circular dichroism of optically active 2,3-dihydro-2-methyl-1,5-benzoxazepin-4(5H)-ones

Summary Chiroptical properties of the title compounds have been studied. The influence of the substitution pattern of the aromatic moiety and the consequence of the amide thioamide conversion are discussed as well.Dedicated to Prof. Dr. W. Wiegrebe on the occasion of his 60th birthday     

Circular dichroism—LXIV : On the chiroptical properties of siccanin derivatives and the absolute configuration of siccanochromene-A

The ¹B_2u-band CD of siccanin (3) and some of its derivatives obeys the known rules for the benzene chromophore with the appropriate substitution pattern. The CD spectrum of the chromanone 8 is better resolved than that of related flavanones, the band between 300–320 nm is most probably the ¹B_2u-band of this chromophore. The non-planar styrenes 10–12 symmetrically substituted in the benzene ring with respect to the “pivot” bond follow Crabbé's rule, and the absolute configuration of siccanochromene-A (13) in the chromene ring follows from its CD to be S.     

α-epithioketosteroids: conformation and reactivity

In order to correlate reactivity with geometry, the conformational analysis of 16,17α-epithiopregnenolone has been carried out using X-ray analysis, low-temperature circular dichroism and quantum chemical calculation. Lack of conformational homogeneity of the acetyl side-chain is revealed; however the conformational equilibrium is restricted to the conformers with relative trans-orientation of epithio- and keto-groups.     

Über die absolute Konfiguration der Cantharsäure und des Palasonins

The absolute configurations of (+)-cantharic acid, a chiral derivative of the achiral insect defensive substance cantharidin ( 1 ), and of palasonin, a lower homologue of 1 occurring in the plant Butea frondosa, were shown to be represented by formulas 2 and 3 , respectively (scheme 1). These results were obtained by application of the Horeau method (table 1) on the (+)-cantharic acid derivatives (+)- 5 , (?)- 7 , and (?) 11 (scheme 2), and the palasonin derivatives (+)- 29 and (+)- 30 (scheme 4), as well as by comparison of the chiroptical properties (tables 2 and 3) of a number of derivatives, prepared from either cantharic acid or palasonin. – Attempts to incorporate various radioactively labelled precursors into palasonin ( 3 ), using young and adult plants, have been so far unsuccessful.     

Spaltungen mittels Diazoniumverbindungen

Zusammenfassung Es wird das Verhalten weiterer phenolischer Stoffe gegenüber Kupplungskomponenten untersucht und damit die Theorie der fördernden Wirkung der -ständigen Heteroatome ausgebaut.     

Oxazepines and thiazepines,XXI: CD-spectra of optically active 2-methyl-2,3-dihydro-1,5-benzothiazepin-4(5H)-ones and related 3-phenylthio-butyric acid derivatives

Summary Chiroptical properties of the title compounds have been studied. The influence of the substitution pattern of the aromatic ring and the configuration of the centre of chirality on the Cotton effects appearing in various wavelengths ranges are discussed.

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Oxazepine und Thiazepine, 21. Mitt.: CD-Spektren optisch aktiver 2-Methyl-2,3-dihydro-1,5-benzothiazepin-4(5H)-one und verwandter 3-Phenylthio-buttersäure-Derivate

Zusammenfassung Die chiroptischen Eigenschaften der im Titel genannten Verbindungen wurden studiert. Der Einfluß des Substitutionsmusters des aromatischen Rings und der Konfiguration des Chiralitätszentrums auf die Cotton-Effekte, die in verschiedenen Wellenlängenbereichen auftreten, werden besprochen.

     

Circular Dichroism and Optical Rotatory Dispersion — Principles and Application to the Investigation of the Stereochemistry of Natural Products

The principles of circular dichroism and of optical rotatory dispersion are described. Examples are given to illustrate the use of these methods for the determination of the configurations and conformations of natural and synthetic products. Some limitations of the octant rule are mentioned.