Equation presented Unprecedented molecular rearrangements during diazomethane-mediated reaction of norbornyl α-ketohemiketals leading to novel molecular entities are presented. A dramatic change in the reaction outcome was noted for five- and six-membered α-ketchemiketals: the former predominantly furnished rearranged bicyclic products involving migration of the γ-alkoxy group, and the latter furnished the oxetane derivative as the major product. Interestingly, six-membered O-methyl-ketal yielded a product arising from the migration of the vicinal alkoxy group © 2007 American Chemical Society.