Ernest Wenkert

Carbon-13 nuclear magnetic resonance spectroscopy of flavonoid and isoflavonoid compounds

Abstract The 13 C NMR spectra of 15 flavonoid and 9 isoflavonoid substances of various ring C oxidiation states were analyzed and their carbon shifts assigned. In the case of 3 terpenic flavones and two glycoflavones linewidths were related qualitatively to molecular segmental motion.

Nickel-induced conversion of carbon–sulphur into carbon–carbon bonds. One-step transformations of enol sulphides into olefins and benzenethiol derivatives into alkylarenes and biaryls

The reactions of alkenyl sulphides, benzenethiols, and aryl sulphides with methylmagnesium and arylmagnesium bromides, mediated by bis(triphenylphosphine)nickel dichloride, in benzene solution have been shown to lead to olefins (predominantly with retention of configuration), toluenes, and biphenyls in medium to high yields.

13C NMR spectroscopy of neolignans

Abstract The 13 C NMR spectra of 15 neolignans of several structural types and two lignans were analyzed and their carbon shifts assigned. The shifts of pyrogallol ether and ethyl phenyl carbinyl ether models were used in this connection. The stereochemistry of a dimeric sideproduct in the preparation of the latter models was determined by 13 C NMR analysis.

Nickel-induced conversion of carbon–nitrogen into carbon–carbon bonds. One-step transformations of aryl, quaternary ammonium salts into alkylarenes and biaryls

Aryltrimethylammonium iodides are shown to undergo reaction with Grignard reagents under phosphine-ligated, low-valent nickel catalysis with the formation of alkylarenes and biaryls.

Synthesis of the Himachalenes by an Intramolecular Diels-Alder Reaction Route

Abstract Cyclization of an acyclic triene in an intramolecular Diels-Alder reaction sense constitutes a one-step production of a bicyclic olefin. Such method of synthesis should find broad acceptance in the field of organic natural products, especially in light of the high desirability of rapid acquisition of complexity of structure.2 The following synthesis of α- and β-himachalene (A and B, respectively)3 illustrates an application of the scheme in the sesquiterpene area.

γ-Ketoacid Derivatives

Abstract It has been shown recently that β-oxycyclopropanecarboxylic esters, prepared by the cyclopropanation of enol ethers with diazoacetic esters, are cleaved easily on acid hydrolysis.3,4 The following discussion illustrates further examples of this two-step procedure of γ-ketoacid synthesis and related reactions.

The structure of gelsevirine

Die Massenspektren und1H- und13C-NMR-Spektren der Gelsemium-Alkaloide Gelsemin, Gelsedin und Gelsevirin wurden aufgenommen und vollständig analysiert. Gelsevirin wurde durch Reduktion in Gelsemin übergeführt und besitzt die Struktur des Na-Methoxygelsemins.

Peptide alkaloids of Discaria longispina

Abstract Three peptide alkaloids have been isolated from Discaria longispina . They include frangulanine and the new substances discarine A (II) and B (III).

Carbon-13 NMR analysis of cyclic peptide alkaloids

Abstract The chemical shifts of the carbons of the peptide alkaloids discarine-A, discarine-B, lasiodine-A, lasiodine-B, pandamine, pandaminine and hymenocardine have been assigned.

Terpenes of Podocarpus lambertius.

Abstract Sitosterol and the following terpenic compounds have been isolated from the bark of Podocarpus lambertius: 3β-hydroxytotarol, 4β-carboxynortotarol, and macrophyllic and lambertic acids. The leaves yielded sitosterol, stigmastan-3β,5α-diol-6-one, isopimaric acid, phyllocladene, isophyllocladene, 8,9-abieten-15-ol and 17-isophyllocladenol.