1% and *H Labelling experiments, together with *H n.m.r. spectroscopy show that 3,5-dimethylorsellinic acid is a specific precursor of austin and terretonin in Aspergillus ustus and Aspergillus terreus, respectively, and so substantiate the mixed polyketide-terpenoid origin proposed for these metabolites from the incorporation of '3C-labelled simple precursors.

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Der ungesättigte Äther (I) liefert bei Behandlung mit überschüssigem Kaliumtert.‐butylat die Cyclisierungsprodukte (II) und (III), die zu (IV) hydriert werden.

C; R1=H,R2=Ph mechanism involving base-catalysed isomerisation of the acetylenic ethers (VIa and b) to allenes, followed by

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