Die Kondensation des Benzimidazolylacetonitrils (I) mit aromatischen Aldehyden (II) liefert die Acrylnitrile (III), die zu den Propionitrilen (IV) reduziert werden.

Glycosylation of the visnagin cleavage product 2 with O‐acetyl‐protected glycosyl donor 5a afforded O‐glycoside 6a, which could be transformed into the O‐benzyl‐protected compound 6b. The latter underwent Fries‐type rearrangement to afford C‐glycoside 4b. The same product could be obtained directly from 2 and O‐benzyl‐protected glycosyl donor 5b. Reaction of 4b with benzaldehyde and anisaldehyde furnished chalcones 7A,B, which, upon treatment with base, furnished flavanone C‐glycosides 10A,B. Selenium dioxide oxidation of 10A,B or of 7A,B led to the corresponding flavone C‐glycosides 11A,B. The same result was obtained by Baker‐Venkataraman rearrangement; on treatment with base, the O‐aroyl compounds 12A–C gave C‐aroyl compounds 13A–C, which, on addition of TMSOTf, furnished flavone C‐glycosides 11A–C. Hydrogenolytic O‐debenzylation of 11A afforded target molecule 3A, which was transformed into O‐acetyl derivative 14A for characterization. Structural assignments of all compounds were based on 1H‐NMR data.

No abstract

Glycosylation of the visnagin cleavage product 2 with O‐acetyl‐protected glycosyl donor 5a afforded O‐glycoside 6a, which could be transformed into the O‐benzyl‐protected compound 6b. The latter underwent Fries‐type rearrangement to afford C‐glycoside 4b. The same product could be obtained directly from 2 and O‐benzyl‐protected glycosyl donor 5b. Reaction of 4b with benzaldehyde and anisaldehyde furnished chalcones 7A,B, which, upon treatment with base, furnished flavanone C‐glycosides 10A,B. Selenium dioxide oxidation of 10A,B or of 7A,B led to the corresponding flavone C‐glycosides 11A,B. The same result was obtained by Baker‐Venkataraman rearrangement; on treatment with base, the O‐aroyl compounds 12A–C gave C‐aroyl compounds 13A–C, which, on addition of TMSOTf, furnished flavone C‐glycosides 11A–C. Hydrogenolytic O‐debenzylation of 11A afforded target molecule 3A, which was transformed into O‐acetyl derivative 14A for characterization. Structural assignments of all compounds were based on 1H‐NMR data.

Bei der Umsetzung der Fluorenderivate (I) mit Arylmagnesiumhalogeniden (II) bildet sich aus dem Dinitril (Ia) neben nur wenig Additionsprodukt (IIIa) in der Hauptmenge das Cyclobutanderivat (IVa), während der Nitrilester (Ib) kein Dimeres (IVb) liefert.