Stereoselective Synthesis of Both Enantiomers of 1,4‐Anhydro‐alditols, 1,4‐Anhydro‐2‐amino‐alditols and D‐ and L‐Isonucleosides from 2,3‐O‐Isopropylidene‐D‐glyceraldehyde Using Iodine‐Induced Cyclization as the Key Step.