Versuche zur enantiomerenreinen Synthese des Chatancins, 1. Mitt. Synthese von (1R,2S,6S,7R,8S,3′S)-2-(4′-Benzyloxy-3′-methylbutoyl)-7-hydroxy-8-isopropyl-1-methylbicyclo [4.4.0]decan-4-on

Summary Our first target on the way towards the synthesis of enantiomerically pure chatancin is the preparation of the title compound. The cycloadduct of 5,5-dimethoxy-1,2,3,4-tetrachlorocyclopentadiene and thymoquinone is stereo- and regioselectively reduced to the tricyclic ketoalcohol4, which by nucleophilic cyclisation and reductive removal of the keto group as well as the chlorine atoms yielded a tetracyclic dimethoxyketal. Acidic hydrolysis freed the keto group, which now was treated with a chiral lithium alkyl compound derived from methyl (R)-2-methyl-3-hydroxypropionate in few steps. The resulting stereomeric tertiary alkohols were fragmented and the decalinones thus obtained separated. X-ray analysis permitted the determination of the absolute configuration of these decalinone derivatives.