SYNTHESIS OF ENANTIOMERICALLY PURE HYDRINDEN-2-ONES AND BENZ[E]INDEN-2-ONES VIA ASYMMETRIC ALKYLATIONS OF CHIRAL BICYCLIC LACTAMS

A route to the titled compounds in >99 % ee was achieved from sequential diastereoselective alkylations of chiral, nonracemic bicyclic lactams 6 and 15. An intramolecular addition of the organolithium species derived from 17a-c and 28a-d gave, after hydrolysis, diketones 25a-c and 30a-d, which were cyclized to the titled compounds 4a-c and 31a-d. As an example of the versatility of this method, the ABC ring system of the triterpene stelliferin A, isolated from marine organisms, was prepared in high enantiomeric excess.