The reaction of 2-keto-1β,4aβ-dimethyl-1α-[2-(3-keto-1,4,4-trimethylcyclohexyl)ethyl]-7-methoxy-1,2,3,4,4a,9-hexahydrophenanthrene1aandbwithp-toluenesulphonic acid in boiling xylene yields the rearranged product, 1,10-dimethyl-2-[2-(3-keto-1,4,4-trimethylcyclohexyl)-ethyl]-7-methoxy-3,4-dihydroanthracene (3). Crystals of3are monoclinic, space groupP21/c,Z = 4, witha = 7.2684(3),b = 30.942(2),c = 10.5544(7) Å, β = 98.24(1)°. The structure was determined by direct methods from diffractometer data and refined by block-diagonal least-squares to anRof 0.043 for 1810 observed reflections. The molecule exhibits no unusual geometric features, although positional disorder is apparent in the cyclohexanone moiety.A possible route for the formation of3from1aandbis presented.