A Novel Synthesis of Oxabicyclo[3.3.1]nonanone via (3,5)-Oxonium−Ene Reaction SahaPipas ReddyU. C. BondalapatiS. SaikiaAnil K. 2010 Oxabicyclo[3.3.1]nonanone can conveniently be prepared by the reaction of <i>trans</i>-<i>p</i>-menth-6-ene-2,8-diol and aldehyde or epoxide mediated by boron trifluoride etherate in good yields. The reaction proceeds via (3,5)-oxonium−ene-type reaction.