(1) 1,9-trans-1,2-cisoid-2,6-cis-4,11,11-Tris(methoxycarbonyl)-6- methyltricyclo[7.4.0.0(2,6)]-tridec-7-ene-4,2-carbolacton e+ ++, C21H26O8, Mr = 406.43, monoclinic, P1, a = 6.0774 (2), b = 12.3784 (5), c = 14.2565 (4) A, alpha = 72.906 (3), beta = 86.361 (3), gamma = 78.181 (3) degrees, V = 1003.38 (6) A3, Dx = 1.345 Mg m-3, Z = 2, lambda (Cu K alpha) = 1.54056 A, mu = 0.82 mm-1, F(000) = 432, room temperature, final R = 0.043 for 2841 observed reflections. The tricyclic compound (1) has the same carbon framework as in the BCD rings in a steroid nucleus. Ring B adopts a chair while ring C has a half-chair conformation. A trans relative stereochemistry is observed at the BC ring junction while a cis hydrinclane is observed for the CD junction, the lactone bridge being cis to the angular methyl group at C(6) and to the hydrogen at C(1).