The Supertristeroids:  Large, Chiral, Molecular Bowls Prepared by Trimerization of Pentacyclic Steroidal Ketones

Robinson annulation of coprostanone (<b>1</b>) at the 2,3- and 3,4-positions gave two pentacyclic enones (<b>7</b> and <b>10</b>) that contain A/B-cis-fused ring junctions. Reduction of these enones gave the pentacyclic steroidal ketones 2α,3β- (<b>8</b>) and 2α,3α-(3‘-oxocyclohexano)-5β-cholestane (<b>9</b>) and 4α,3β- (<b>11</b>) and 4α,3α-(3‘-oxocyclohexano)-5β-cholestane (<b>12</b>). The structures of compounds <b>8</b>, <b>9</b>, and <b>11</b> were unambiguously established by X-ray analysis. TiCl<sub>4</sub>-promoted trimerization of compounds <b>8</b> and <b>11</b> gave the “supertristeroids” <b>4</b> and <b>5</b>, respectively:  large (C<sub>93</sub>) chiral, hydrocarbon clefts with <i>C</i><sub>3</sub>-symmetric pockets approximately 12 Å in diameter.