Enantiomorphous tri-o-thymotide clathrates of prochiral oxiranes were submitted to the action of gaseous hydrogen halides. Ring-opening reactions ensued that differ from those reported in homogeneous phase, showing a considerable modification of the chemical reactivity of the external reagent in the host lattice. Chirality transfer from the host receptors to the guest products was also observed, but with a poor efficiency. Gaseous hydrogen halides promote the rearrangement of prochiral enclathrated epoxides to allylic alcohols in contrast to the base-catalyzed analogous reaction in the liquid state. Chirality transfer from the host lattice to the guest products is observed.