A mild access to chiral syn 1,2-diaryl glycols by stereoselective ring opening of ortho substituted trans 2,3-diaryl-oxiranes using Amberlyst 15 in H2O/THF system

Amberlyst 15 was an efficient and green catalyst for the reaction of 2,3-diaryloxiranes with H2O in organic co-solvent to prepare glycols in high yield. Ortho substituted trans 2,3-diaryloxiranes afforded the corresponding syn glycols stereo- and enantiospecifically. Stereoselectivity appeared related to the coordination ability of the substituents, irrespective of their electronic properties. Indeed o-OCH3 and o-OBn substituted syn glycols were obtained in high stereochemical ratios (6/1 and 10/1, respectively), and o-OTIPS and o-NO2 substituted ones were obtained as exclusive products, with the same ee of the parent epoxides.