Cyanide ion acts as a nucleophile and attacks the carbonyl group of the methyl ketone forming a cyanohydrin ion, which on attack by ethanol ion leads to formation of carboxyl group and on further hydrolysis forms an ester. The alkanide ion from the grignard reagent then attacks the carbonyl of ester twice to form a diol with two alcohol groups attached to a 3o carbon. The sequence of reactions are given below:





