Synthesis of Bridgehead Substituted Bicyclo[2.2.1]Heptanes. Radical Cyclization of an Oxime Ether and an α,β-Unsaturated Ester

The synthesis of bicyclo[2.2.1]heptanes with useful functionality at each bridgehead is achieved by radical cyclization of appropriately substituted 4-methylene- and 4-benzyloxyimino- cyclohexylmethyl radicals. The latter process, for example, leads to a bridgehead amine. Optimum yields are achieved when the reactions are conducted at 110� with slow addition of tributyltin hydride; under these conditions, the uncyclized isomer is either not detected, or formed in very small quantity. Production of a mixture of five- and six-membered cycloalkanones from similar treatment of the analogous 4-oxocyclohexylmethyl radicals reveals that the reaction is medicated by the corresponding 1-norbornyloxy radical.