Radical Cyclizations Leading to the Bicyclo[2.2.1]heptane Framework: A New Radical Approach to (+-)-(Z)-(beta)-Santalol

Tandem radical cyclizations of acyclic iodides, including [3-(2-iodoethyl)6,10-dimethyl-undeca-5,9-dien-1-ynyl]-dimethylphenylsilane lead in good yields to bicyclo[2.2.1]heptane derivatives. The cascade relies on two sequential radical-mediated 5-exo-cyclizations. The radical approach is illustrated with the total synthesis of racemic-(Z)-(beta)-santalol. The results are remarkable, two fused rings and one stereogenic center are formed in a single operation. A new ‘coordinated’ hydride appeared to be useful in the cascade.