A practical ortho-rearrangement of silyl group of ortho-bromophenyl silyl ethers using magnesium(0)

A practical synthesis of ortho-silyl-substituted phenol from ortho-bromophenyl silyl ethers without using RLi is described. Various ortho-bromophenyl silyl ethers are treated with commercially available Mg turnings, which are easy to handle in air, and transfer of the silyl group to the ortho-position occurs in good to high yields. Selective mono-magnesiation of 2,6-dibromophenyl silyl ether is observed even in the presence of excess Mg, and ortho-bromo-6-silylphenol is obtained as the predominant product. The obtained ortho-silyl-substituted phenol is formylated with (CH₂O)_n/MgCl₂/Et₃N, and then condensation with a diamine leads to a silyl-substituted salen-type ligand in a good yield. This scheme is suitable for the large scale synthesis of silyl-substituted salen-type ligands bearing imine groups.