Even if is difficult enough to synthesize acetal, (K<1) there's a range of acetal that have a extra contribution to their stability given to their cyclic structure. Is the same contributed we saw in cyclic hemiacetal synthesis. To synthesize a cyclic acetal we need a diole, and the cycle will form if composed by 5,6 or 7 terms.
Here's the mechanism of the reaction:
The steps are the same we saw in the synthesis of acetals.
