# Stereo selective reaction products

Pyruvic acid on reduction with yeast gives (-) lactic acid while with $\ce{NaBH4}$ it reduces to (+) lactic acid. How?

I know this has something to do with stereoselectivity. But I don't know which one would be a correct answer.

It would be more helpful if you could explain a bit about stereo-selective reactions. I know what it is, what I want to know is, how to find which of the products will be stereochemically preferred one, just like in this question.

• There is no way that borohydride reduction of pyruvic acid can give anything other than racemic lactic acid. – iad22agp Oct 25 '15 at 22:50