4,5-secocholest-3-yn-5-one

(3R,3aR,5aS,6R,9aS,9bS)-6-But-3-ynyl-3-(1,5-dimethyl-hexyl)-3a,6,7-trimethyl-1,2,3,3a,4,5,5a,6,9a,9b-decahydro-cyclopenta[a]naphthalen-9-one