No abstract

Pyrolysis of a dihydroxylactone 2b, prepared by oxidation of the levopimarie acid-formaldehyde adduct 1, unexpectedly resulted in decarboxylation to methyl 13a-hydroxy-14-oxoabietan-18-oate (5) or to methyl 8 , 14adihydroxy-12-abieten-18-oate (8) depending on the conditions. Decarboxylation of methyl 12a-carboxy-13ahydroxy-14-oxoabietan-18-oate (4a) also gave 5. These remarkable and unusually facile decarboxylations were traced to a degenerate acyloin rearrangement in 13-hydroxy-14-oxoabietanes which involves reversible migration of the C-12-C-13 and C-8-C-13 bonds. In the methyl ester 4b, prepared by treatment of 2b with methanolic HC1, the stable orientation of the carbomethoxy group was shown to be axial. Transformations of 5 and 8 which shed light on the stereochemistry of various 14-oxygenated abietanes are described.

Im Zusammenhang mit Untersuchungen an Harzsäuren wird u.a. aus dem Lävopirnarsäure‐Formaldehyd‐Addukt (I) durch Oxidation die Dihydroxy‐Verbindung (II) hergestellt, die bei der Pyrolyse je nach den angewandten Bedingungen zu (III) oder (IV) führt.

Oxidation von (I) mit Kaliumpermanganat/Natronlauge und anschließende Diazomethan‐Veresterung ergibt das Diol (II) und das Diollacton (IV).

The transformation of the readily available levopimaric acid-formaldehyde adduct 3a to the title compound lb by a convenient five-step sequence is described. Four of the steps proceed in quantitative or nearly quantitative yield. The first step involves an unusual oxidation of a cyclic ether to a 6 lactone in the presence of a secondary hydroxyl group. In the last step three reactions, reductive elimination of an aeetoxy group, (3 elimination of an acyloxy function, and decarboxylation, are effected at once.