Why does fructose reduce Tollen's reagent and Fehling's solution?

Question

Even though fructose is a ketohexose (ketone-containing hexose, a six-carbon monosaccharide), it reduces Tollen's reagent and Fehling's solution. Generally, a ketone does not reduces Tollen's reagent and Fehling's solution. So, why is this possible in the case of fructose?

Answer 1

Ketoses will rearrange to aldoses under basic conditions, via something called the enediol rearrangement. It is discussed here: https://www.masterorganicchemistry.com/2017/09/12/reducing-sugars/ . I assume this type of rearrangement is much faster in ketoses than typical ketones because all the hydroxyl groups enhance the acidity of hydrogens alpha to the carbonyl.