Metal-Free Reductive Cleavage of Benzylie Esters and Ethers: Fragmentations Result from Single and Double Electron Transfers

摘要

The reductive deprotection of benzyl ethers 1 to form alcohols 2, and of benzyl esters 3 to form carboxylic acids 4 are widely used transformations (Scheme 1). Approaches to these transformations include hydrogenolysis (H2 with cata- lyst), and electron transfer, either by electrolysis or through homogeneous reduction under Birch conditions. More recently, a method involving the use of SmI2 in the presence of a tertiary amine and water has been developed by the group of Hilmersson for the cleavage of benzyl-heteroatom bonds.This work is quite complementary to the cleavage studies of benzoate esters 5, recently reported by Lam and Marko, where the regiochemistry of fragmentation of intermediate ester ketyls is controlled by the reaction conditions.