Cyanohydrins, functionalized Grignard reagent protection

The cyanohydrin not only adds an additional C at the site of the C==0 but also introduces two new functional groups, OH and CN. which can be used to introduce other functional groups. The OH can be used to form an alkene (C=C), an ether (—RO), or a halogen compound (C—X) the C N can be reduced to an amine (CHjNHj), be hydrolyzed to a carboxyl (COOH) group, or react with Grignard reagents if the OH is protected. 

---