1 contains a keto group and a carboxylic acid group. When 1 is treated with a reducing agent, three reactions are possible.
When 1 is treated with the reducing agent sodium borohydride (see hydride reagent), the only organic product observed is 2.
Evidently, sodium borohydride reacts with only one of the two functional groups in 1. Thus, the reaction of 1 with sodium borohydride is chemoselective.
see also regioselective, stereoselective