In a recent organic chemistry lab, I attempted to reduce benzil to meso-hydrobenzoin with sodium borohydride and eventually water (a rather simple undergrad lab). I understand most of the chemistry behind the reaction, but I find myself wondering why the meso form of hydrobenzoin predominates. I believe the formation of the first asymmetric center affects the production of the second, but I cannot seem to come up with a mechanism that explains the results. According to some sources, there is a cyclic borate ester intermediate during the reaction, but I do not understand how that intermediate actually forms. Any help at all would be greatly appreciated.