Expedient, High-Yielding Synthesis of Silyl-Substituted Salen Ligands

Described is an efficient synthesis of silyl-substituted salen ligands, used for the preparation of enantioselective catalysts. The salicylaldehyde precursors are synthesized from the silyl ethers of 2,6-dibromophenols via a one-pot double lithium halogen exchanges, to induce an intramolecular retro-Brook rearrangement and allow introduction of the aldehyde group. Condensation of the salicylaldehyde products with a chiral diamine affords the silyl-substituted salen ligands in high yields. The use of other electrophiles allows easy access to silyl-substituted phenolic esters, ketones, and boronic acids.