An organocatalytic method for the asymmetric synthesis of syn-1,3-dioxanes as protected 1,3-diols via dynamic kinetic resolution of in situ generated chiral cyanohydrins has been developed. This method involves a reversible cyanohydrin formation/hemiacetalization/intramolecular oxy-Michael addition reaction cascade, affording a chiral syn-1,3-diol structure with simultaneous construction of two stereogenic centers. The use of trifluoromethyl ketones is crucial for the efficient three-component cascade reaction, and a chiral bifunctional organocatalyst imparts high enantio- and diastereoselectivities in the formation of the chiral syn-1,3-diol motifs.