Complex examples of the Dowd-Beckwith rearrangement: a free radical route to 2-oxabicyclo [3.3.0]octan-3,6-diones

The synthesis of 8-iodooxabicyclo[3.2.1]octanes from substituted benzoic acids via a reductive alkylation-halolactonization sequence is described. These iodolactones were converted to 2-oxabicyclo[3.3.0]octane derivatives upon treatment with either allyltri-n-butylstannane or tri-n-butylstannane via a process that involves a Dowd-Beckwith rearrangement. The scope and limitations of this process are discussed. (C) 2001 Academie des sciences / Editions scientifiques et medicales Elsevier SAS.