Absolute configuration of vouacapen-5α-ol

The title compound, C20H30O2, {systematic name: (4aR,6aS,7R,11aS,11bR)-4,4,7,11b-tetramethyl-1,2,3,4,4a,5,6,6a,7,11,11a,11b-dodecahydrophenanthro[3,2-b]furan-4a-ol}, is a cassane furanoditerpene which was isolated from the roots of Caesalpinia pulcherrima. The absolute configurations at positions 4a, 6a, 7, 11a and 11b are R, S, R, S and R, respectively. The molecule has four-fused rings consisting of two cyclohexane rings, one cyclohexene ring and one furan ring. The cyclohexane and cyclohexene rings are trans-fused. Two cyclohexane rings are in chair conformations, while the cyclohexene ring is in an envelope conformation. In the crystal structure, the molecules are linked by intermolecular O—H...O hydrogen bonds into a zigzag chain along the a axis. A short O...O contact [3.0398 (14) Å] is also present.