Eine neue Synthese von (±)-Pyrenophorin

A new Synthesis of (±)-Pyrenophorin The synthesis of pyrenophorin (I), a 16-membered dilactone metabolite of plant pathogenic fungi is described. Reaction of the Grignard reagent II with the activated succinic acid ester III gave the methyl (t-butyl)dimethylsilyloxy-oxo-octanoate IV which was converted into the corresponding ethylene acetal. Dehydrogenation via the benzeneselenenyl derivative lead to pyrenophorinic acid V with protected functional groups. Selective removal of silyl group followed by saponification of the ester group provided the ethylene acetal-hydroxy acid VI suitable for the cyclodimerisation reaction. This was effected with azodicarbonic acid ester and triphenylphosphine at ?40° in a dilute toluene solution. The 16-membered dilactones VII with protected carbonyl groups were isolated in 24% yield. Silver-ion induced cyclodimerisation of the S-2-pyridyl carbothioate of VI gave much lower yields. Removal of the acetal groups lead to (±)-pyrenophorin (I) and meso-pyrenophorin in about equal amounts.     

Eine neue Synthese von Dihydrofuryliumsalzen

Ohne Zusammenfassung     

Synthese von (±) Seychellen

A four step synthesis of Seychellene ( 1 ) is described. Intramolecular Diels-Alder reaction of dienon 2 furnished the tricyclic ketones 3 and 4 in good yield. Hydrogenation of 3 gave 5 and 6 . The higher reactivity of 6 with methyllithium compared to 5 allowed the selective preparation of 8 , which, on subsequent acid-catalyzed rearrangment afforded Seychellen in 57,5% yield. In an analogues manner epi-Seychellene was synthetized via the intermediates 5 and 7 .     

Eine neue Synthese von Nornarcein

N-benzylnornarceine-ethyl ester hydrochloride (3a) and N-benzylnornarceinehydrochloride (4a), both obtained byHofmann degradation of N-benzylnarcotinium bromide (2), are debenzylated catalytically to nornarceine-ethylester-HCl-salt (5) and nornarceine (6).Die HCl-Salze von N-Benzylnornarcein-äthylester (3a) und N-Benzylnornarcein (4a), erhältlich durchHofmann-Abbau aus N-Benzylnarcotiniumbromid (2), werden katalytisch zu Nornarcein-äthylester-Hydrochlorid (5) und Nornarcein (6) entbenzyliert.     

Eine neue Synthese von Petalin

A new synthesis of the alkaloid petaline ( 14 ), which includes a Stevens rearrangement ( 5→6 ) and the preferential O-demethylation of 6 , is described. The structures of the by-products in the demethylation were determined by the use of nmr. and mass spectroscopy.     

Eine neue Synthese von 1,2,3-Triphenylbenzol

Ohne Zusammenfassung