Totalsynthese optisch aktiver Steroide. XIII. Mitteilung. Synthese von 4,9(11)‐Androstadien‐3,17‐dion

Synthesis of 4,9(11)‐androstadiene‐3,17‐dione. The total synthesis of 4,9(11)‐androstadiene‐3,17‐dione ( 23 ) is described starting from (1 S , 7 a S )‐1‐ t ‐butoxy‐7a‐methyl‐5,6,7,7a‐tetrahydroindan‐5‐one ( 8 ) as a CD‐building block. The key step involves alkylation of 8 with 1‐chloro‐7,7‐ o ‐phenylenedioxy‐octane‐3‐one ( 14 ) a novel AB‐synthon to give the diketone 15 . 15 is converted to the secosteroid 20 via the diene enol ether 17 using a previously described procedure. Low temperature methylation of 20 affords predominantly the 10β‐methyl compound 21 , which is readily transformed into the title dione 23 .