Adamantane Rearrangement of [3.3.2]Propellanes

For elucidation of the isomerization pathway of the [3.3.2] propellane ring system into “adamantaneland” by effective skeletal transformations, hydride-transfer reduction of [3.3.2]propellanols [(exo-4) and (endo-4)] and [3.3.2]propellene (5) was carried out. It was found that tricyclo[5.3.0.01 2348]decane (6) was obtained as a sole initial product in 25, 32, and 38% yields, respectively. Similar reaction of 1,7-trimethylenenorbornanol (9) furnished 6 in a 27% yield, and AlCl3-catalyzed rearrangement of 1,7-trimethylenenorbornane (12) gave 6 as well as adamantane (2) and exo-tetrahydrodicyclopentadiene (3). Moreover, 6 readily isomerized to 2 with H2S04 or A1C13. These results indicate that the adamantane rearrangement of the [3.3.2]propellane ring system follows the route [3.3.2]propellane → 12 → 6 →2.