text: 15-Crown-5 can be synthesized using a modified Williamson ether synthesis:
  :(CHOCHCHCl) + O(CHCHOH) + 2 NaOH → (CHCHO) + 2 NaCl + 2 HO
  It also forms from the cyclic oligomerization of ethylene oxide in the presence of gaseous boron trifluoride.