Optimized Catalytic Enantioselective Aryl Transfer Process Gives Access to mGlu2 Receptor Potentiators

An asymmetric enantioselective aryl transfer reaction was developed to give access to the diarylmethanol 7 and ultimately acetate 2 which is useful for the preparation of mGlu2 receptor potentiators (Scheme ). The aryl transfer chemistry involved the preparation of a proposed arylalkylzinc species 14 from boroxine 16 and diethylzinc (DEZ), and reacting this mixture with aldehyde 5 in the presence of chiral ligand 15. During the course of optimizing the preparations of proposed intermediate 14 and diarylmethanol 7, an understanding of optimal stoichiometry and reaction times was gained through empirical observation, the use of solution IR, and analyzing off-gases via real time gas analysis/mass spectroscopy. The preparation of diarylmethanol 7 and subsequent conversion into acetate 2 required carefully selected workups, selective extractions, and azeotropic distillations to generate a series of stock solutions to accommodate oil intermediates that finally gave acetate 2 as a crystalline solid with >99% ee.