Synthesis of Bridgehead-Substituted Bicycloheptanes by Radical Cyclization

Article abstract of DOI:10.1021/jo00060a029

A kinetic investigation shows that the rate of cyclization (k_C) of the (4-methylenecyclohexyl)methyl radical 3 at 25 deg C is 4.4 x 10² s^-1, which is considerably slower than that (2.3 x 10⁵ s^-1) of the parent 5-hexenyl radical.The energy of activation for the process 3 -> 4 is 12.8 kcal mol^-1, which is in excellent agreement with theoretical values derived from force-field calculations.Ring-closure of appropriately substituted (4-methylenecyclohexyl)methyl radical precursors allows the synthesis of bicyclo<2.2.1>heptyl systems with useful functionality at the bridgehead to be achieved readily and in high yield.An interesting example is given of the application of an iodine-atom-transfer cyclization to the synthesis of a bicyclo<2.2.1>heptane functionalized at C7 and C1.