Steroide und Sexualhormone. 261. Mitteilung. Quassinoide Bitterstoffe II. Partialsynthetischer Zugang zu Quassin: Überführung von Testosteron in eine Schlüsselverbindung mit angulärer 8β‐Methylgruppe

Partial Synthesis of Quassin: Synthesis of a Key Intermediate with an Angular 8β‐Methyl Group from Testosterone A key intermediate in the partial synthesis of quassin (1) was synthesized in 28 steps starting from testosterone (9) (Scheme 3). The key features are: (i) The conversion of testosterone (9) into the 1α, 2β, 3β‐O‐substituted 4α‐methylandrostane 19 (Scheme 3) and its transformation into an intermediate 26 with the ring A partial structure of quassin (Scheme 4). (ii) The conversion of 19 to the vinylogous α‐hydroxyketone 5 (Scheme 6 and 7). (iii) The photochemically induced [2+2]‐cycloaddition of allene to hydroxyenone 5, affording the 8β, 14β‐cyclobutano‐derivative 6 (Scheme 2 and 8). (iv) The conversion of 6 into the key compound 7. In connection with this last transformation a new method for the degradation of phenylselenoesters of carboxylic acids to the corresponding nor‐alkanes was developed (see Scheme 8). Details of this reaction will be published elsewhere [18].