Helvetica Chimica Acta

For the characterization of organic substances in gas chromatography a number termed «retention index» is proposed. A simple relation exists between the retention index of a compound on a non‐polar stationary phase and its boiling point.

The proton NMR spectra of 265 steroids of known structure have been recorded for 0,1M solutions in deuterochloroform and the positions of the signals of the 18‐and 19‐hydrogen atoms have been measured. The additional chemical shifts due to various substituents at many different positions of the steroid skeleton are compiled in a table. With its help most chemical shifts of the 18‐ and 19‐hydrogen atoms of these and unknown steroids may be computed with an accuracy of ± 0,015 ppm. An example show how to calculate the chemical shifts. The physical basis of teh influences due to substituents and double bond, as well as the reasons for the generally small deviations from the calculated chemical shifts, are reviewed and illustrated. The additional chemical shifts due to identical funcitonal groups in equivalent positions, i. e. in approximately the same steric relation to one of the tertiary methyl groups, are collected in a table. Possible reason for teh variation of these additional chemical shifts within sets of identical functional functional groups in equivalent positions are discussed. The table furnishes interesting insights into the conformation of certain steroids and shows the average values and deviations one has to reckon with if the chemical shifts on methyl groups in non‐steroidal compounds due to functional groups in corresponding positions to those in steroids are to be computed.

An extensive study and analysis of the concepts, classification, presentation, and nomenclature of chirality and lack of chirality in crystal structures and their constituents is presented. Oriented crystal structures are classified. The chirality rules for existence of molecular crystal structures are examined and the relation to segmentation and latent symmetry highlighted. The nomenclature of chirality and related terms, and the relationship of chirality to optical activity is covered. The uses and limitations of the Euclidean normalizer are treated. An improved glossary of terms is included.

The Michael‐additions of aliphatic, alicyclic, and arylsubstituted nitroolefins and enamines lead to γ‐nitroketones 3 in good chemical and excellent (> 90%) diastereomeric yields (see Table 1).

The known threo‐configuration of one type of adducts 3 (entries 8, 10, and 11 of Table 1) can be arrived at by assuming the approach 8 of the Michael‐acceptor and ‐donor; the reaction follows a topological rule, which is formulated and which is applicable to such diverse reactions as the diene synthesis, cyclopropanations, carbonyl olefinations and methylenations, aldol‐ and nitroaldol‐type additions, as well as additions of lithium, boron, and chromium derivatives to aldehydes (see 9, 10, 11, and Table 2).

Fadenmolekeln hochpolymerer Stoffe, welche in ruhender Lösung eine statistisch wahrscheinlichste Gestalt (loses Knäuel) haben, erfahren in strömender Lösung nicht nur Richtungsänderungen der Fadenachse; vielmehr werden durch die von der strömenden Flüssigkeit ausgeübten Kräfte auch Änderungen der Gestalt, insbesondere Änderungen des Abstandes h zwischen Molekelanfangs und ‐endpunkt erzwungen.

The cyclic urea DMPU (N, N′‐dimethyl‐N, N′‐propylene urea = 1,3‐dimethyl‐2‐oxo‐hexahydropyrimidine) is shown to exhibit the same effects HMPT in oxirane‐opening with Li‐acetylide, in a Wittig olefination, in the double deprotonation of nitroalkane, in the Michael addition of Li‐dithiane to cyclohexenone, and in selective generations of certain enolates (Schemes 1–7) DMPU might therefore be as safe substitute of the carcinogenic HMPT as a cosolvent with unique properties in diverse type of reaction.

A rapid and inexpensive method for the large‐scale purification of C₆₀ is the simple filtration of the toluenesoluble extract of commercial fullerene soot through a short plug of charcoal/silica gel with toluene as the eluent. Reactions of C₆₀ with ethyl and tert‐butyl diazoacetates in refluxing toluene lead to the formation of the (alkoxycarbonyl)methylene‐bridged isomers 1a–3a and 1b–3b, respectively, which can be equilibrated, upon further heating, into the single compounds 1a and 1b, respectively. Isomers 1a/b possess the methano bridge at the 6–6 ring junction, whereas structures 2a/b and 3a/b are bridged at the 6–5 junction. A dramatic influence of local and π‐ring current anisotropic effects of the fullerene sphere on the NMR chemical shifts of the methine protons in the bridge is observed: the chemical shifts of the protons located over a pentagon ring in 2a/b and over a hexagon ring in 3a/b differ by Δδ = 3.47 and 3.45 ppm, respectively. The analysis of the ¹³C‐NMR chemical shifts of the bridgehead C‐atoms and the ¹J(C,H) coupling constants for the methano‐bridge atoms reveals conclusively that the 6‐5‐ring‐bridged structures 2a/2b and 3a/3b are π‐homoaromatic (‘open’ transannular bond) and the 6‐6‐ring‐bridged structures 1a/b are π‐homoaromatic (‘closed’ transannular bond). The electronic absorption spectra show that π‐homoconjugation in 2a/b and 3a/b represents a much smaller electronic perturbation of the original C₆₀ chromophore than σ‐homoconjugation in 1a/b. The results of this study demonstrate an impressive linkage between the chemistry of methano‐bridged annulenes and methano‐bridged fullerenes.

Carbocyclic Compounds from Monosaccharides. 1. Transformations in the Glucose Series

A method for the preparation of pentasubstituted cyclopentanes from monosaccharides is presented, involving two crucial steps, viz. the reductive fragmentation of 5‐bromo‐5‐deoxyglucosides (such as 10, 17 and 23, see Scheme 3) with Zn or butyl lithium yielding 5,6‐dideoxy‐hex‐5‐enoses (such as 11 and 24, see Schemes 3 and 4), and the subsequent cyclization of these hexenoses with N‐methyl‐ or N‐(alkoxyalkyl)hydroxylamines (via the corresponding nitrones) to form cyclopentano‐isoxazolidines (see Scheme 2). Thus, the glucosides 17 and 23 were converted diastereoselectively and in good yields into the cyclopentano‐isoxazolidines 27 and 45 (Schemes 5 and 7), which were characterized by their transformation into various derivatives. 27 and 45 were correlated through the common derivative 62. The configuration of the cyclization products were established by pyrolysis of the N‐oxide 65 to the enol ether 67 (Scheme 10).

A general chemical phosphorylation method based on P(III) chemistry has been developed. The system is demonstrated for the phosphorylation of oligonucleotides, directly after their synthesis on a solid support, and for the O‐phosphorylation of serine, threonine, and tyrosine as well as for a serine‐containing peptide.