Lutz Weber

1,3-Dipolare cycloadditionen von 6,7-dialkoxy-3,4-dihydroisochinolinium-Salzen

Zusammenfassung Die 1,3-dipolaren Cycloadditionen von 6,7-Dialkoxy-3,4-dihydroisochinoliniumalzen mit Dipolarophilen vom Azomethin- und Alkentyp wurden untersucht. Die Regioselektivitat der Reaktion wird mit Hilfe der Perturbations-Theorie unter Verwendung von CNDO/2 und CNDO/S Programmen gedeutet. Die Rechnung steht nur dann in allen Fallen mit den experimentellen Daten im Einklang, wenn im Ubergangszustand ein Abstand von 3 A zwischen den Molekulen angenommen wird. Das Auftreten von exo/endo-Addukten wird interpretiert.

Elucidation of the structure of an unusual cyclic glycolipid from Torulopsis apicola

Abstract The yeast Torulopsis apicola produces a microcrystalline mixture of glycolipids, the major component of which has been identified as the novel 16-(2′- O -β- d -glucopyranosyl-β- d -glucopyranosyloxy)hexadecanoic acid 1′,4″-lactone 6′,6″-diacetate ( 2 ) by spectroscopic methods.

Oxygenation of Hexadecane in the Biosynthesis of Cyclic Glycolipids in Torulopsis Apicola

Biotransformation of [1-13C] labelled hexadecane, hexadecanol and hexadecanoic acid have been investigated using the yeast Torulopsis apicola. The yeast produces a microcrystalline mixture of two glycolipids, the lipophilic moiety of which consists of ω- or (ω-l)-hydroxylated hexadecanoic acid. Biosynthesis of these glycolipids takes place via hydroxylation of hexadecane, oxidation to hexadecanoic acid and ω or (ω-l)-hydroxylation of hexadecanoic acid. Feeding the cell cultures with a mixture of hexadecane and [1-13C] labelled hexadecane derivatives one observes 13C enrichment ratios which indicate that neither of the biohydroxylation or oxidation steps are rate limiting in the formation of the glycolipids, furthermore, two different monooxygenase systems appear to be involved in hydroxylation of hexadecane and hexadecanoic acid.

Photocatalytic oxygenation of α-pinene with molecular oxygen activated by niobium and molybdenum porphyrins: Part LXX1. Photocatalytic systems

Abstract The photocatalytic oxygenation of α-pinene using tetraphenylporphinatomolybdenum and niobium complexes and molecular oxygen results in the formation of pinene epoxide and oxygenated products derived from an allylic hydrogen abstraction mechanism. The formation of radical intermediates was verified by ESR and spin-trapping experiments.

Photocatalytic oxygenation of strained alicyclic alkenes with µ-oxo-bis[tetraphenylporphyrinatoiron(III)] and molecular oxygen

Iron(III) porphyrins are active catalysts for the photocatalytic epoxidation of strained cyclic alkenes and their methyl substituted derivatives with molecular oxygen.

A new route to 1,3,4-thiadiazolines. Part 3. Consequences of the aza-enamine concept

N,N-Disubstituted hydrazones react with sulphenyl chlorides, sulphur dichloride, and disulphur dichloride to give C-sulphenyl products. N,N-Tetramethylenehydrazones with SCl2 or S2Cl2 give the novel pyrrolo[2,1-b]-1,3,4-thiadiazole ring system. Studies of the site selectivity in reaction of these hydrazones with sulphur(II) electrophiles by the semiempirical CNDO and MNDO methods are reported.

1,3-Dipolar cycloaddition reaction of 3,4-dihydro-6,7-dimethoxyisoquinoline ylide with olefins

2-Methoxycarbonylmethyl-3,4-dihydro-6,7-dimethoxyisoquinolinium ylide (2) in a concerted cycloaddition reaction of type π4s+π2s with dimethyl fumarate and dimethyl maleate gives the (4a)‘endo’-, (4b)‘exo-’, and (6a)‘endo’-pyrrolo [2,1-a] isoquinoline derivatives, respectively. The structure and conformation of the products have been determined by 1H, 13C, and 15N n.m.r. spectroscopy and X-ray diffraction for compound (4a).

Photocatalytic enantiodiscriminating oxygenation with cyclodextrin-linked porphyrins and molecular oxygen

2,6-Permethylated β-cyclodextrin-linked iron and manganese porphyrins catalyse the enantioselective oxygenation of a racemic mixture of (S)-α-pinene and (R)-α-pinene with molecular oxygen under irradiation with visible light.

Zuordnung offenkettiger Diastereomerer mittels lanthanoiden-induzierter Verschiebungen (LIS)

The LIS method has been tested for assignment purposes of acyclic diastereomers. After the estimation of the coordination geometry Eu ... O for some alkyl-methyl-ethers, the ground state conformations of the coordinated substrates have been determined and related to the free substrates. Due to obtained differences, the application of the LIS method for present assignment purposes should be limited to strained, less flexible stereoisomers.