Ortho-hydroxyalkylaton of phenol substrates was performed via coordinative complexes of metal phenolates with chiral glyoxylates: optically active 2-hydroxymandelic esters have been obtained with good yields and very high diastereoselectivity (up to 94% d.e.).
Stereoselective Synthesis of Optically Active 2-Hydroxymandelic Acids and Esters via Friedel−Crafts Coordinated Reaction: Crystal Structure of Chiral Dichloro[2-(1-oxido-1-menthoxy- carbonylmethyl)-4-methoxyphenoxido-<i>O</i>,<i>O</i>,<i>O</i>]titanium
Hydrolysis or reduction of the esters 3 afforded 2-hydroxymandelic acids 6 and diols 5 in high yields and enantiomeric pure form. Mechanistic evidence of chelation-controlled reaction comes from the crystalstructure determination of titanium phenoxide complex 8.