Synthesen in der Isochinolinreihe: Zur Ätherspaltung 6,7,8-trimethoxy-substituierter Isochinolinverbindungen mit wässeriger Salzsäure

Zusammenfassung Die Behandlung des 6,7,8-trimethoxy-substituierten 1,2,3,4-Tetrahydroisochinolins (I) mit 20proz. wäßr. HCl ergibt zur Hauptsache das entsprechende 6,7,8-Trihydroxyderivat II. Die Behandlung des analog substituierten 3,4-Dihydroisochinolins IV und Isochinolins XXI führt hauptsächlich zu den 6,8-dimethoxy-7-hydroxy-substituierten Isochinolinverbindungen V und XXII, unter selektiver Spaltung der in 7-Stellung befindlichen Methoxyl-gruppe. Die Konstitution von V und XXII konnte durch Synthese und Abbau bewiesen werden.

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Treatment of the 6,7,8-trimethoxy-substituted 1,2,3,4-tetrahydroisoquinoline I with 20% aqueous HCl yields predominantly the corresponding 6,7,8-trihydroxy derivative II. The analogously substituted 3,4-dihydroisoquinoline IV and isoquinoline XXI are converted into their 6,8-dimethoxy-7-hydroxy derivatives V and XXII under these conditions. The constitution of these phenols was established by synthesis and degradation.

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Herrn Prof. Dr.H. Bretschneider zum 60. Geburtstag gewidmet.     

Synthesen der diastereoisomeren Caparrapioxide

Syntheses of Diastereoisomeric Caparrapi oxides. Two pathways have been developed for the synthesis of caparrapi oxide from the dihydroionones. The four diastereoisomeric racemates and their dehydro- and dihydro-derivatives are described. NMR. spectra indicate that the sesquiterpene ethers having cis-fused rings exist in two different conformations.     

Synthesen der Nonactinsäure

Two stereoselective syntheses of nonactic acid I, the building block of the macrotetrolide antibiotic nonactin are described. The characteristic cis-configuration of the 2,5-substituents on the tetrahydrofuran ring of I is obtained in the first synthesis by catalytic hydrogenation of the furan derivative X. This key intermediate possesses the carbon skeleton and correct distribution of oxygen functions for conversin into nonactic acid. It is synthesized by an electrophilic substitution of 2-acetonylfuran (VI) with the N-cyclohexyl-N-propenyl nitrosonium ion (V) generated from the corresponding α-chloronitrone (VII) and silver fluoroborate, followed by hydrolysis and oxidation of the aldehyde group. The second synthesis starts with a diol already having the correct configuration of the side chain that contains the hydroxyl group. For this purpose threo-1-octen-5,7-diol (XV) is synthesized from acetylacetone in two steps. Oxidative cleavage of the terminal double bond of this threo-diol yields an aldehyde which is converted by a Wittig reaction, with the carbanion, obtained from diethyl α-methoxycarbonylethyl phosphonate, into the open chain intermediate, 2-methyl-6,8-dihydroxy-2-nonenoic acid methylester (XVIII). Base-catalyzed cyclisation of this α,β-unsaturated dihydroxy ester yields the methyl ester of nonactic acid (I) as the main product.     

Synthesen in der Naphthalinreihe: Methoxylierte Tetralone und Naphthole

Ohne ZusammenfassungHerrn Prof. Dr.A. Franke in aufrichtiger Verehrung zum 80. Geburtstag gewidmet.