Serendipitously discovered diazomethane-mediated novel molecular rearrangements of norbornyl alpha-ketohemiketals.

[reaction: see text] Unprecedented molecular rearrangements during diazomethane-mediated reaction of norbornyl alpha-ketohemiketals leading to novel molecular entities are presented. A dramatic change in the reaction outcome was noted for five- and six-membered alpha-ketohemiketals: the former predominantly furnished rearranged bicyclic products involving migration of the gamma-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.