1,7-Trimethylenenorbornane. A novel member of the ‘adamantaneland’. Preliminary communication

A synthesis of the novel C₁₀H₁₆ hydrocarbon 1,7-trimethylenenorbornane ( 13 ), one of the 19 members of the adamantane family, is described.     

‘One-Pot’ Synthesis of Raumacline from Ajmaline

For the alkaloid raumacline ( 2 ), which is a biotransformation product of ajmaline ( 1 ) in Rauwolfia serpentina cell cultures, an efficient ‘one-pot’ synthesis was developed using a NaBH₄/riboflavin/light-mediated transformation of 1 into 2 with a total yield of 86%.     

Der ‘Push-Pull’-Effekt von ‘Push-Pull’-Oligoacetylenen. Eine 13C-NMR-Untersuchung

The ‘Push-Poll’ Effect of ‘Push-Pull’ Oligoacetylenes. A ¹³C-NMR Investigation According to ¹³C-chemicaI shifts of ‘push-pull’ oligoacetylenes 1 – 4 , the ‘push-pull’ effect (i.e. π delocalization induced by ‘push-pull’ substituents) rapidly decays in this series. To correct for other than π -charge-density effects, Δδ values of symmetrically placed C-atoms of the oligoacetylene chain are discussed. Stereoelectronic resteffects (SER) of the substituents on terminal C-atoms of PP-ketones 1a – 3a and PP -esters 1b – 4b are estimated from the residual Δδ of the asymptotes of Fig. 3. Fig. 4 convincingly shows that Δδ values are dramatically decreasing with increasing number n of acetylene units between the push and pull substituents. Assignment problems of ‘push-pull’ triacetylenes 3 have been solved by ¹³C labelling of the CO group of 3a .     

The Enantioselective Synthesis of the ‘Southern Part’ of Soraphen A

Using a series of enantioselective aldol condensations followed by an ester enolate addition, the cyclic hemiacetal 2 was prepared stereospecifically. Hemiacetal 2 represents the synthetically most challenging ‘southern part’ of the antifungal macrolide soraphen A ( 1 ). Spontaneous enolisation of 26 , the C(2) epimer of 2 , revealed that 2 is the most stable diastereoisomer at room temperature.     

Synthese von ‘D-Isothreonin’ und ‘L-Alloisothreonin’ aus L-Alanin

Synthesis of ‘D -Isothreonine’ and ‘L -Alloisothreonine’ Starting from L -Alanine Starting from L -alanine, ‘D -isothreonine’ ( = (2R, 3S)-3-amino-2-hydroxybutanoic acid) and ‘L -alloisothreonine’ ( = (2S, 3S)-3-amino-2-hydroxybutanoic acid) were synthesized.     

Synthesis of cyclosporine. Total syntheses of ‘cyclosporin A’ and ‘cyclosporin H’, two fungal metabolites isolated from the species Tolypocladium inflatum GAMS

The heptapeptide H-MeBmt-Abu-Sar-MeLeu-Val-MeLeu-Ala-OBzl ( 20 ) was synthesized for coupling with the previously described cyclosporine tetrapeptide sequence Boc-D -Ala-MeLeu-MeVal-OH ( 21 ). The product of the coupling, the undecapeptide Boc-D -Ala-MeLeu-MeLeu-MeVal-MeBmt-abu-Sar-MeLeu-Val-MeLeu-Ala-OBzl ( 22 ), was then deprotected and cyclized to cyclosporine ( 1 ). The tetrapeptide diastereoisomer Boc-D -ala-MeLeu-MeLeu-D -MeVAl-OH ( 23 ) could also be used as a starting material to produce selectively the desired undecapeptide 22 . In this case, the N-methyl-D -valine unit, was selectively isomerized to the L-from by using the appropriate condensing agent. The diastereoisomeric undecapeptide Boc-D -ala-MeLeu-MeLeu-D -MeVal-MeBmt-Abu-Sar-MeLeu-Val-MeLeuAla-OBzl ( 24 ) was also synthesized starting from 21 by using the mixed pivalic anhydride method to selectively invert the configuration of the N-methyl-L -valine. The structure of the undecapeptide 24 was confirmed by deprotection and cyclization to ‘cyclosporin H’, a natural product known to have the structure [D -MeVal¹¹]cyclosporine ( 2 ).     

A novel synthesis of α-sulfenylated aldehydes

Ketones are converted into α-sulfenylated aldehydes with addition of one carbon atom via reaction with methoxyphenylthiomethyllithium followed by rearrangement of the adducts.     

Lithium Enolates: ‘Capricious’ Structures – Reliable Reagents for Synthesis

The first part of this review article deals with the structures of enolates. The development of research in this field during the last half century will be illustrated by highlightening seminal contributions, while, by no means, an attempt of comprehensiveness is made: the choice of spotlights has, admittedly, a personal touch. Aside from derivatization of lithium enolates and their crystal structures that meanwhile are classics, more recent solution studies are presented. In the second part, it will be shown by contributions of our laboratory that, despite their complicated structures, lithium enolates are reliable ‘workhorses’ in synthesis with emphasis being given to stereoselective C? C bond forming reactions due to the Pd‐catalyzed allylic alkylation of non‐stabilized, preformed enolates.     

The ‘even-electron rule’

Many (>170) exceptions to the ‘even-electron rule from the literature (unrecognized in most cases) and from the authors’ laboratory are presented and discussed. The large number of violations suggests that although the generalization may be a helpful guide for the explanation of mass spectral behaviour of many organic compounds, the term ‘rule’ seems to be unjustified.     

Oligosaccharide Analogues of Polysaccharides. Part 12. Synthesis of ‘acetyleno-saccharide’-derived cyclodextrin analogues

‘Acetyleno-oligosaccharides’ in which two terminal ethynyl substituents enclose an angle (significantly) below 180° are building blocks for the preparation of cyclodextrin analogues. This is illustrated by the preparation of a cyclotrimer and a cyclotetramer; the C₃-symmetrical cyclotrimer 18 (Scheme 1) was synthesized in 13 steps (7.7%) and the C₄-symmetrical cyclotetramer 51 (Scheme 3) in 14 steps (4.3%) from the known dialkyne 21. The solubilities of 18 and 51 in H₂O were determined by gravimetry; a saturated solution is 130 mM in the trimer 18 and 12.8 mM in the tetramer 51 . The dependence of the optical rotation of 18 and 51 in H₂O on the concentration, and the concentration dependence of the ¹H-NMR chemical shift of the signals of the ¹CH groups of 51 (D₂O) suggest that there is no significant self-association of 18 and 51 .     

A comparison of classical and quantum-mechanical ‘ring-current’ theories

The proton resonance spectra of a series of 2,7-disubstituted-4,5-bis(2-pyridyl)phenanthrene-3,6-diols are examined with emphasis on the shielding effects produced by aromatic ‘ring currents.’ In this series, two pyridine rings are rigidly held less than 3.4 Å apart and with considerable overlap. The ‘ringcurrent’ shieldings found for above-the-plane positions are in good agreement with the Johnson-Bovey theory, whereas a recently proposed quantum-mechanical theory underestimates the shieldings by a factor of nearly three.     

‘Lone Pair’ and ‘CI Bond’ Ionization Energies of exo- and endo-2-Norbornyl Iodides

A PE-spectroscopic study of exo- and endo-2-norbornyl iodides suggests that the relative ability of the 2-norbornyl group to stabilize an electron deficiency on a substituent X (e.g. I) in exo- or endo-position depends on the location of the positive charge. There is no difference if the positive hole is strongly localized on on the substituent X (e.g. the 5p^?1 state of the title compounds). On the other hand, our results indicate that teh positive hole semi-localized in an exo-C? X bond is better stabilized by the 2-norbornyl group than a semi-localized, positive hole in an endo-C? X bond.     

Enantioselective Synthesis of α-N-Alkylamino Acids via Sultam-Directed ‘Enolate’ Hydroxyamination

Crystalline N-hydroxyamino-acid derivatives 4 , readily available from non-chiral acyl chlorides 2 and sultams 1 , were treated with aldehydes in the presence of NaBH₃CN to give N-alkylhydroxylamines 5 . N,O-Hydrogenolysis of 5 and saponification of 6 furnished (S)-N-alkylamino acids 7 in high optical purity. Similarly, (R)-N-alkylamino acids 12 were obtained from the antipodal acylsultams 8 .     

Synthese von ‘Push-Pull’-Diacetylenen

Synthesis of ‘Push-Pull’ Diacetylenes The first synthesis of push-pull diacetylenes of type 1 is described. Reaction of perchlorobutenyne ( 8 ) with two equivalents of dialkylamine, followed by dechlorination using two equivalents of butyllithium gives lithio-dialkylamino-diynes 7 . Final acylation of these intermediates leads to push-pull diacetylenes 1b–1e in good yields. The method allows the introduction of both push and pull substituents in a simple one-pot-procedure. In addition, 1a is prepared by hydroxymethylation of lithio-morpholino-diyne 7c , followed by oxidation with manganese dioxide in acetone.     

Ion cyclotron resonance spectrometry. A means of evaluating ‘kinetic shifts’

Ion Cyclotron Resonance Spectrometry Is Proposed As The Method For Evaluating ‘Kinetic Shifts.’ The Proposal Is Tested By A Comparison Of The Appearance Potentials For Some Simple Cleavage Reactions With Those For Some Cleavage And Rearrangement Fragmentations In Benzene, Benzonitrile, Anisole, Aniline And Cubane.     

Facile synthesis of polypyridine esters: A route to functionalized aldehydes

A wide range of ester-substituted oligopyridines, based on pyridine, 1,8-naphthyridine, 1,10-phenanthroline, 2,2'-bipyridine, and 2,2':6', 6' '-terpyridine units, has been synthesized and fully characterized. The principal reaction involves the palladium(0)-catalyzed carboalkoxylation of the bromo-, chloro- or triflate-substituted pyridine unit with carbon monoxide in the presence of a primary alcohol as nucleophile and a tertiary amine as base. Monofunctionalization of disubstituted compounds is realized by reaction in ethanol under mild conditions (70 degrees C, 1 atm CO). Stepwise reduction of selected esters with sodium borohydride, followed by Swern oxidation, affords the corresponding carbaldehydes in good yield. Several products are reported for the first time. The synthetic methods reported herein represent a valuable approach to the large-scale preparation of ester-functionalized oligopyridines that can be subsequently transformed to the corresponding alcohols or acids. These procedures also provide a practical methodology to the rational design of ligands bearing different kinds of functionalities.     

Synthese von ‘Push-Pull’-Oligoacetylenen

Synthesis of ‘Push-Pull’-OligoAcetylenes ‘Push-pull’ triacetylenes 11a , b , c , as well as ‘push-pull’ tetraacetylene 13b have been prepared by reaction of the corresponding trichloroene(oligoinyl)amines 9 and 10 with 2 mol-equiv. of BuLi followed by acylation. The sequences (Schemes 3 and 4) are very simple and straightforward, they could in principle be applied to the synthesis of ‘push-pull’ pentaAcetylenes 15 and hexaacetylenes 17 (Scheme 5). Main limitations are the moderate yields as well as the low thermal stability of push-pull oligoacetylenes.